Everytime i start the engine the computer will not drop the rpm's to normal, after the warming period has been completed.anybody knows?

Engines rarely idle at the same rpm all the time. Its normal for changes to occur, especially small ones. Too many variables that can effect such a small change to list. Its no an issue to worry about.

The truck ECM computer controls the idle speed based on a number of engine parameters. Idle drops to a minimum preset level when engine coolant reaches normal operating range and the engine goes into closed loop control. This idle is typically set at around 575 rpm, and cannot be changed without reprogramming the ECM. The miss is not caused by the idle speed - unless the engine is tuned properly and has not lost compression, this idle speed can result in a rough running engine at idle (typical with older 4.3L Vortec engines). Best bet is to get a complete tuneup which will include checking the O2 sensors, catalytic converter and cleaning the IAC valve and throttle body.

Go to auto zone they check for free, then will know what's is next.

First we would need to know when this occurs. Asuming the oil level is at the full mark!. If the pressure goes up during acceleration and down at idle when engine is fully warmed up, then this is normal. An engine requires 10 psi of oil pressure per 1,000 rpm ( ex. 20 psi at 2,000 rpm, 25 psi at 2,500 rpm, and so on ) . If the gauge is moving back and forth erratically at idle , i would say the gauge is bad. If it drops to 0 while accelerating I would say your oil pump is bad. If from time to time it seems to work and other times it seems not to work, I would say the oil pressure sending unit for the gauge is bad. If the pump failed you would start to here a Knocking noise from the engine in a short period of time. Use the above scenario's to narrow down what it may be.

First we would need to know when this occurs. Asuming the oil level is at the full mark!. If the pressure goes up during acceleration and down at idle when engine is fully warmed up, then this is normal. An engine requires 10 psi of oil pressure per 1,000 rpm ( ex. 20 psi at 2,000 rpm, 25 psi at 2,500 rpm, and so on ) . If the gauge is moving back and forth erratically at idle , i would say the gauge is bad. If it drops to 0 while accelerating I would say your oil pump is bad. If from time to time it seems to work and other times it seems not to work, I would say the oil pressure sending unit for the gauge is bad. If the pump failed you would start to here a Knocking noise from the engine in a short period of time. Use the above scenario's to narrow down what it may be.

First we would need to know when this occurs. Asuming the oil level is at the full mark!. If the pressure goes up during acceleration and down at idle when engine is fully warmed up, then this is normal. An engine requires 10 psi of oil pressure per 1,000 rpm ( ex. 20 psi at 2,000 rpm, 25 psi at 2,500 rpm, and so on ) . If the gauge is moving back and forth erratically at idle , i would say the gauge is bad. If it drops to 0 while accelerating I would say your oil pump is bad. If from time to time it seems to work and other times it seems not to work, I would say the oil pressure sending unit for the gauge is bad. If the pump failed you would start to here a Knocking noise from the engine in a short period of time. Use the above scenario's to narrow down what it may be.

This is normal, as long as the rpm's are not above 2000, this is to heat the engine to it's operating temperature quickly. Once the engine is warm, the rpm's will drop to 600-800RPM.

sounds like you have to adjust your idle, fuel injected or carburated?

This may been an ignition module or a MAF sensor, this car may need to be diagnosed using a OBD I computer code reader to accurately diagnose the problem.

Check engine codes.
If it comes up as a Crankshaft sensor... Replace it.
These are the exact symptoms