Excelerator pedal flat to the floor max RPM 2500 at a speed 100 klms but on slight incline speed falls back between 70 / 90 klms with RPM at 2000
Have replaced the total exhaust system including c/c, spark plugs, oxygen sensor, fuel filter, computer checked for arking, throttle body reset, idle reset
Runs well until engine gets to normal working temperature, the engine does not over heat, the auto gear box c6 has been checked.

 

I'm not as much a mechanic as others on this site but I would check the compression. Sounds like the motor is worn out with the information you have given.

Is 2500 rpm the max you can get out of it if your floored?

 

I'd check for codes there's a how-to in the stickies, it's a good place to start. Also some info on your truck like what engine and year.