I was driving and my battery gauge was up to 19, a mechanic said the alternator was overcharging, so had that fixed and put in new battery, then it ran fine except when i turned anything on heater and light the gauge would go down to 11 and the lights would dim, replaced the serpintine belt and ran ok, but now when i warm it up in the morning or at stop sign it dont want to stay running and kinda putters, but if i am going down the road it is fine, codes came up for 02 sensors replaced both of them and the mapsensor, and ran ok for a day, now its doing it again not wanting to stay running at idol and no check engine light is on..any ideas where to go from here?

Change the alternator

I would need to know what year the Jeep is to comment on the overcharging problem as well as the code 37 problem.
There could be a voltage regulator on the alternator, or it could be built into the engine computer.

if the alt. was overcharging may have damaged the cluster

Your car's symptoms (voltage fluctuations under load that shouldn't happen) seem to
strongly indicate that your voltage regulator has failed. The voltage regulator is the component
that regulates voltage coming from the alternator, and which is supplied to the rest of the car.
Your new belt tensioner indicates to me (and should have to your mechanic) that the
alternator and/or voltage regulator weren't able to operate properly, and a faulty belt tensioner
has killed more than one car's alternator/voltage regulator.
Your do not need new headlights. Do fix the turn signals.

In the 2005 Sunfire, the voltage regulator is an integral component of the alternator, and is
not separately serviceable. So your 2005 Sunfire needs a new alternator.

2005 Pontiac Sunfire Alternator - Duralast Part Number: DL2305-15-4 $199.99 available at:
http://www.autozone.com/autozone/parts/2005-Pontiac-Sunfire/Alternator/_/N-jmqtpZ93xme

The national parts chains (Advance Auto Parts, AutoZone, Pep Boys) will (for free) administer
a "Charging System Test." Which will telly you for sure that your alternator/voltage regulator
is bad. Do this before replacing alternator, since its a pricy part in the 05 Sunfire.

Just in case, Here's the 2005 Sunfire manual entry on (a) Diagnosis & testing the alternator, and
(b) replacement of the alternator

Alternator replacement is a do-it-yourself project, though you may need to get a
"Serpentine Belt Kit" on your favorite parts store's loan-a-tool program to remove/re-install the serpentine (drive) belt.
======================================================================
Diagnosis & Testing - 2005 Pontiac Sunfire Alternator


Alternator Load Test

1. With the engine running, turn on the blower motor and the high beams ( or other electrical accessories to place a load on the charging system).

2. Increase and hold engine speed to 2000 rpm.

3. Measure the voltage reading at the battery.

4. The voltage should increase at least 0.5 volts from the voltage test. If the voltage does not meet specifications, the charging system is malfunctioning.
NOTE
Usually under and overcharging is caused by a defective alternator, or its related parts (voltage regulator), and replacement will fix the problem; however, faulty wiring and other problems can cause the charging system to malfunction. Many automotive parts stores have alternator bench testers available for use by customers. An alternator bench test is the most definitive way to determine the condition of your alternator.




Alternator No-Load Test

1. Connect a tachometer to the engine.
CAUTION
Ensure that the transmission is in Park and the emergency brake is set. Blocking a wheel is optional and an added safety measure.


2. Turn off all electrical loads (radio, blower motor, wipers, etc.)

3. Start the engine and increase engine speed to approximately 1500 rpm.

4. Measure the voltage reading at the battery with the engine holding a steady 1500 rpm. Voltage should have raised at least 0.5 volts, but no more than 2.5 volts.

5. If the voltage does not go up more than 0.5 volts, the alternator is not charging. If the voltage goes up more than 2.5 volts, the alternator is overcharging.
NOTE
Usually under and overcharging is caused by a defective alternator, or its related parts (regulator), and replacement will fix the problem; however, faulty wiring and other problems can cause the charging system to malfunction. Many automotive parts stores have alternator bench testers available for use by customers. An alternator bench test is the most definitive way to determine the condition of your alternator.


6. If the voltage is within specifications, proceed to the next test.



Voltage Test

1. Make sure the engine is OFF , and turn the headlights on for 15-20 seconds to remove any surface charge from the battery.

2. Using a DVOM set to volts DC, probe across the battery terminals.

3. Measure the battery voltage.

4. Write down the voltage reading and proceed to the next test.



Removal & Installation - 2005 Pontiac Sunfire Alternator


2.2L (VIN 4) Engines

1. Before servicing the vehicle, refer to the precautions section.

2. Remove or disconnect the following:

Negative battery cable

Accessory drive belt

Alternator mounting bolts

Alternator electrical connectors

Alternator





To install:

1. Before servicing the vehicle, refer to the precautions section.

Alternator. Torque the upper bolts to 37 ft. lbs. (50 Nm) and the lower bolt to 22 ft. lbs. (30 Nm).

Alternator electrical connectors

Accessory drive belt

Negative battery cable





2.2L (VIN F) Engines

1. Before servicing the vehicle, refer to the precautions section.

2. Remove or disconnect the following:

Negative battery cable

Accessory drive belt

Alternator mounting bolts

Alternator electrical connectors

Alternator





To install:

1. Install or connect the following:

Alternator. Torque the bolts to 16 ft. lbs. (22 Nm).

Alternator electrical connectors

Accessory drive belt

Negative battery cable

Over charging could be the result of several things including:

Faulty Voltage Regulator
1. A car's battery will overcharge if the voltage regulator isn't working correctly. A voltage regulator is usually part of the alternator, and is used to keep a steady flow of voltage to the battery. If the voltage regulator is defective, it will send either too little or too much charge to the battery. If it sends too much, the car battery will overcharge. The voltage regulator is easily replaceable at an easily affordable price, sometimes for as little as twenty dollars, as of 2009.
Faulty Alternator
2. Sometimes the alternator itself can be at fault. The alternator is the device that converts the mechanical power of the engine into electrical power to charge the battery. When an alternator breaks, it usually stops creating electricity for the battery, which will then eventually die. However, if the wrong alternator is placed in the car, or if the alternator is running at the wrong pace, it will create too much energy for the car battery, causing it to overcharge. The alternator is another easily replaced part.
Incorrect Charger Use
3. If a battery charger is used to charge your battery outside of your car, improper use of the charger can result in overcharging. If a battery is placed on the charger too long, it can result in overcharging, and a significant decrease in your battery's lifespan and efficiency. This is why it is important to read about your specific battery and understand how long it needs to charge to be effective. Too much charge will lead to problems.
Faulty Battery Chargers
4. Sometimes chargers can be faulty. Their settings may be wired incorrectly, or the charges labeled incorrectly. As a result, your battery may be getting overcharged, even if you are carefully monitoring your charging. This is a problem that is hard to avoid, as manufacturing mistakes can happen anywhere, anytime without warning. It is a good idea to test your charger regularly to see if it is running correctly.
Heat
5. Extreme heat in the summer can also have an adverse effect on the car battery. If the battery has been previously overcharged, extreme heat can increase the problems caused by overcharging, and exacerbate any other problems with the battery. This problem can be hard to avoid if you live in a warm climate. The only real way to ensure safety against this problem is to avoid overcharge in the first place.

check the alternator output

either the "new" (more likely rebuilt) alternator is overcharging, (17+ volts) or the diodes are defective and the alternator is putting out AC volts instead of DC volts

put a new regulator on and dont use secondhand bits from scrapyard

get a volt meter set it on dc scale start your engine .take meter hook it to battery it should be 13.5 to 14.5. it shouldnt go over 15. if it goes over 15 volts your alternator has a bad voltage regulator. take it back get you a new one.

You might want to call the dealer.
I think there was a service bulletin to replace the connectors in the back of the instrument cluster