I have a 1996 Chevy Silverado c3500 with 7.4 it is running -18 long term fuel trim both banks and -8 short term both banks goes to -25 it and-10 st when rpm increases to 3000 possibly causes

You don't say what engine ,does it have E85 flex fuel .assume USA vehicle ?

Fuel Trim
The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. The ECM monitors the heated oxygen sensor (HO2S) signal voltage while in Closed Loop and regulates the fuel delivery by adjusting the pulse width of the fuel injectors based on this signal. The ideal fuel trim values are around 0 percent for both short term and long term fuel trim. A positive fuel trim value indicates the ECM is adding fuel in order to compensate for a lean condition by increasing the pulse width. A negative fuel trim value indicates that the ECM is reducing the amount of fuel in order to compensate for a rich condition by decreasing the pulse width. A change made to the fuel delivery changes the short term and long term fuel trim values. The short term fuel trim values change rapidly in response to the HO2S signal voltage. These changes fine tune the engine fueling. The long term fuel trim makes coarse adjustments to the fueling in order to re-center and restore control to short term fuel trim. A scan tool can be used to monitor the short term and long term fuel trim values. The long term fuel trim diagnostic is based on an average of several of the long term speed load learn cells. The ECM selects the cells based on the engine speed and engine load. If the ECM detects an excessive lean or rich condition, the ECM will set a fuel trim diagnostic trouble code (DTC).

What code P0000 ?

Fuel Trim Index
Fuel Trim
%
0% +/- 10%

Lean condition bank 1 refers to the computers interpretation of information delivered by the o2 sensor for bank 1. Possible causes are many. First look at the sensor readings. You should see a fluctuation of voltage readings. If the sensor is not fluctuating it should set another code with it. The readings should be .05 v to about .455 volts normally. If the readings are lean then look at the fuel trims. They will likely be nowhere near 0. When the engine is right, the trims may go positive 3 to negative 3. If your short term fuel trim is say +18 and the long term fuel trim is say +20 at idle then try runnung the engine at a steady 1600 rpm and wait a minute till the readings level out. If they approach 0 then look for a vacuum leak. Let the engine idle and use choke cleaner spray to find the leak. Spray suspect areas and watch for changes in fuel trims.

po171 system too lean bank one first chek freeze frame data if code was set at cold engine subzero temp you may need reseal the intake on best scenario you have a vacuum leak affecting bank one double chek your fuel trims short term if adding fuel 2 digits look for vacuum leak if none foun unplug your uuper o2 for that bank and recheck trims any cheapy scan tool do this not until your trims are on short term +-3 at least this code will set if problem only in one bank do not replace maf sensr

Hi there:Here's the printout from the diagnostic tool. Year: 2006Manufacturer: ChryslerMake: DodgeModel: DurangoEngine Type: V8, 4.7LTransmission: AutomaticTrim Level: SLTMileage: 127555 KMs
=== Stored Error Code(s) ===Error Code: P2074Possible Causes: Manifold Absolute Pressure/Mass Air Flow - Throttle Position Correlation at Higher LoadError Code: P0068Possible Causes: MAP / MAF - Throttle Position Correlation
Freeze Frame Information:1. DTC for which Freeze Frame was Stored - P2074.2. Fuel System 1 Status - Closed Loop.3. Fuel System 2 Status - Closed Loop.4. Calculated LOAD Value - 74.51 percent.5. Engine Coolant Temp - 199.40 degrees F.6. Short Term Fuel Trim - Bank 1 - -3.91 percent.7. Long Term Fuel Trim - Bank 1 - -3.13 percent.8. Short Term Fuel Trim - Bank 2 - 0.78 percent.9. Long Term Fuel Trim - Bank 2 - -4.69 percent.10. Intake Manifold Absolute Pressure - 22.21 Inhg.11. Engine RPM - 2,404.00 Rpm.12. Vehicle Speed Sensor - 73.94 Mph.13. Ignition Timing Advance #1 Cylinder - 25.50 degrees.14. Intake Air Temperature - 64.40 defrees F.15. Absolute Throttle Position - 31.37 percent.16. Time Since Engine Start - 1212 Sec.17. Commanded EGR - 7.06 percent.18. EGR Error - 0.00 percent.19. Commanded Evaporative Purge - 62.35 percent.20. Fuel Level Input - 93.73 percent.21. Barometric Pressure - 26.35 Inhg.22. Control Module Voltage - 14.35 V.23. Absolute Load Value - 0.00 percent.24. Commanded Equivalence Ratio - 0.00.25. Relative Throttle Position - 0.00 percent.26. Ambient Air Temperature - -40.00 degrees F.
Monitor Information:1. MIL - OFF.2. Misfire Monitor - Complete.3. Fuel System Monitor - Complete.4. CCM Monitor - Complete.5. Catalyst Monitor - Complete.6. Heated Catalyst Monitor - Not Supported.7. EVAP Monitor - Complete.8. Secondary Air System Monitor - Not Supported.9. O2 Sensor Monitor - Complete.10. O2 Sensor Heater Monitor - Complete.11. EGR Monitor - Complete.12. NMHC Monitor - Not Supported.13. Nox Adsorber Monitor - Not Supported.14. Boost Pressure System Monitor - Not Supported.15. Exhaust Gas Sensor Monitor - Not Supported.16. PM Filter Monitor - Not Supported.

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.
Thank you for using FixYa.

Code Po171 indicates a lean condition on cylinder bank #1 of the engine. This is the drivers side of the engine. I would suggest replacing both front oxygen sensors as a pair to start. An oxygen sensor has a life span of about 5 years and yours are now 9 years old if they are original. When they get older they are slow to respond to changes in the oxygen content of the exhaust and can trigger a code Po171. If you continue to have the same code set after the replacement of both oxygen sensors then it is time to find out why your engine is running lean. Some of the most common causes are an ignition misfire and a vacuum leak. I have also seen Fords EGR flow sensor (known by Ford as Delta Pressure Feedback sensor) to cause problems like that as well. A good mechanic with a scan tool can usually spot a problem like that in a few minutes.

Because you got a misfire on cylinder #1 PO301
A misfire on cylinder #2 PO302
Misfires first 1000 rev PO316
O2 Codes PO 174
Etc,Etc


The LTT, is the result of not learning (yet-thus long term)
what isn't working correctly---Your Engine

Replace bad Coil--which ever is missing
Do not go by the codes,alone ,TEST

If the computer is bad than it will need to be replaced.

I would make sure the bank 1 sensor 1 O2 sensor is not stuck lean. I have run into this many times. Usually you can unplug the sensor and have the vehicle runs better and watch the bank 1 short term fuel trims settle down a bit. You will need a higher end scan tool to view O2 sensor data and fuel trim data so its not necessarily DIY friendly but maybe something for the shop to check if they have not checked already.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa