The EGR vale is new, it it is rough idoling or driving..i drive about 104 miles a day..it use about 1/4 tank gas per trip. (new plugs) they are fowled out .. i pulled the wires one ata time no change in running..i noticed also the transmission kicks in a lot (to high--passing gear) ...al

You'll need to know how big the fuel tank is on your truck. They used different sized tanks depending on the box or body fitted. I think the standard body box was a 26 gallon tank and the long body box was a 34 gallon. This will help you work out your actual miles per gallon.
That model's factory figures have it at between 12 to 13 mpg average. How and where you drive your truck can also affect you fuel consumption quite a lot, City driving, Hard accelerating, Lots of steep hills where you drive and Driving Off Road all can ruin you MPG figures. Using the your numbers that does seem a little lower than it should be. When was it last given a full service? Have you changed fuel supplier, (different gas station). All of these affect MPG Do you have any warning lights on the Dashboard? Use the comment button below with more information and I'll try to help you more.

Using your numbers here's the math.
26 gallon tank - half tank = 13 gallons. 34 gallon tank - half tank = 17 gallons. You got 104 miles.
Sum used is 'Miles achieved divided by the number of gallons used'.
(26 tank) 104 divided by 13 = 8 Mpg.
(34 tank) 104 divided by 17 = 6 Mpg.

Plug wires on wrong ?
Timing belt jumped ?
Exhaust Converter blocked? They only last 12 to 14 years (maybe)
Plugs Gaped correctly?
Vacuum leaks-Evap,Exhaust,Intake,PCV !!
Egr problem?

set trip odometer to zero,fill fuel tank,drive car until 1/2 tank and fill up again record your miles from trip odometer, divide this number by the gallons of gas you just filled car with and this will give you miles per gallon (MPG)

One tank of gas is not enough to compare mileage. Or are you saying the computer's readout of mpg estimate is showing less? Try a tank or two of premium and see if that helps. Keep track of gas mileage. Driving techniques have a lot to do with gas mileage, as does long trips vs. short trips, highway cruising vs. city driving. For best mileage, do regular maintenance and keep the car in top running condition-good spark plugs and clean filters and clean oil ! Attend to minor problems before they escalate.
If you want to check actual miles per gallon, start with a full tank. Write the odometer reading down, and go. Everytime you put gas in, write down the amount. When you are close to 1,000 miles from the time you started, go fill the tank and include that amount of gas to your previous list. Now add up all the gas used and divide it into the miles to get miles per gallon. (976 miles/31.8 gallons = 30.69 mpg ) . Only one tank will skew your numbers, might be off cause the tank was filled more to the top than the previous fill-up. About a thousand miles of driving will give you a very accurate figure of miles per gallon for your car.

It sounds like you may have an EGR valve sticking open. That can also cause the p0171 code, which means fuel system lean, and the p0401 which is insufficient EGR flow, kinda sounds like the valve may just be stuck open and not moving at all. replace the EGR valve.

there is a book publish by the govnt or minister of transport on the exact milage as well if you know how many liters or gallons go in your tank like 80 liters and the gas is 1.00 a liter it cost $80 for 80 liters on a full tank you do 500 km but make sure proper conditions of 100km a hour tires all proper equal pressure the wind is also a facture there is a lot involved to calculate your gas proformance as well if you had a oil change done latly you can find out on a govt site for gas consuption or consumers report

Your car should average roughly 32.5 mpg-US (7.24 L/100 km; 39.0 mpg-imp)

1. change air filter. 2 check timing. 3 check all fuel lines and connections for leakage. 4. dirty or clogged injectors.

could be either a bad thermostat or a plugged fuel filter try them first

My Answer:

Poor gas mileage can be a result of many many things.

First of all you need to find out what is the factory normal gas mileage for your model year Jeep SUV. It should have said on your window sticker if you bought it brand new. If you are a 2nd or 3rd owner then a Jeep dealer would have info. Google search will tell you as well, and only takes a couple minutes to find.

I did a quick Google search and for a 2003 Jeep Grand Cherokee with a (4.7L V8 engine) the average mileage is roughly 14 mpg.

Not sure what engine you have as to options, etc?

How you drive will greatly change that number up or down depending on a number of driving and driver variables.

A few being -

Driving habits?

Tire pressures?

Engine tuned up?

Lube & oil/filter changes (every 5,000-7,500 miles? Air filter changes (every 10,000-15,000 miles)? Read your auto manual for exact recommended intervals.

How many people in the SUV on average?

Are you towing anything?

Type gas you are burning - BRAND? (See injectors below)

Area you are driving in (hills and valleys verses flat out,
etc)

Jeeps in general don't have a good track record for great mileage, and rough engine idling is always a clue that your fuel injectors are dirty. Typical on all Jeeps with port fuel injection systems! On Jeeps with dirty fuel injectors your mileage will go way down accordingly. If your not putting at least a 12 oz bottle of say Walmart brand Super Tech Fuel Injector Cleaner (~ $1 each) in your gas tank religiously every logged 1000 miles, or every 2 tank fill ups, then you are just inviting dirty fuel injectors and POOR fuel economy!

My 1993 Ford XPLR with a 4L V-6 engine (and ~ 160,000 flawless driven miles) gets roughly 22 miles per gallon on the highway with cruise control on, and about 17 around town on average. I religiously put a 12 oz bottle of the above injector cleaner in my gas tank every 1000 miles!! Of course I do all my own tune-ups, general repairs, and suspension maintenance (shocks, O2 sensors, trans oil changes, lube & oil/filter changes, code reading and clearing, etc) myself and it shows! I don't trust repair shops except for say Tires and Balancing at SEARS.

Hope that helps ease your mind about gas mileage as it relates to your Jeep there.

Frank