I have a 04 silverado base model with the 4.3 and 5 speed. while driving as I shift sometimes the engine rpms either increase or remain where they were when I shifted and other times the rpms drop like they are supposed to. This is driving me nuts.

 

is the engine not dropping or the tachometer, it is a big difference and i have a hard time believing that the engine is not dropping rpm cause then an upshift would be impossible

 

The engine.

 

And as far as checking the fluids, they are good, and the air filter well it is about time it should be changed, but i have not physically looked at it. This truck has been doing this for at least a year now, with the same air filter in it.

 

when it happens how long does it increase and it might to clean the cat out of the contanmins sorry if i spelled it wrong or get the crap out of the cat

 

i am assumeing this is a stick but you know what happens when you assume

 

oops my bad yes it is a 5 speed

 

How long have you been having this problem?

 

This could just be the clutch going bad. As pressure declines, the engine has to work a little harder to do the same job.

Is the shifter properly adjusted?

Actually, it's a little hard to tell from the original post if the shifting is the problem, or the tachometer is merely not registering the shift and responding.

 

clutch, try starting out in 3rd gear, if it doesnt want to move then the clutch is weak, if it starts moving under protest or dies the clutch is good, just dont burn it up, i bet the pressure plate springs are weak