1996 K1500 Manual Transmission

[crsgmc]

This is going to sound strange.....but starting truck and idle are fine. Put it in gear and accelerate normally and in any gear then remove food from gas petal the truck is still going strong. Push in the clutch and it is running at 2000 rpm some times it will drop back down but most of the time you need to stop the truck and it will return to 700 rpm idle. A few times I got it to do it in the garage in neutral reving it up to 1500 or 2000 and it started going crazy. Sometimes when cruzing with foot off the gas petal (when it is running down the road at 1500 to 2000) it speeds up and slows down. I replaced the throttle position sensor and the idle air control valve and it did nothing. Cleaned the MAF did not help so unplugged MAF and it ran a little worse but the problem remained as before. Cleaned the intake this did nothing. It is not throwing any codes. I also inspected the throttle cable and it works smoothly no binding or sticking. About a year ago I installed a new gm 350 crate engine and at that time I replaced a lot of parts dist, wires, plugs, fuel filter,new injectors, most sensors etc. I ran fine until this problem came up. What am I missing? Someone must have had this problem before.

Thank You For Any Help You Can Provide.