Problem with 96 2500 5-speed

I have a 96 K2500 5-speed with an idle problem. When you are driving and go to shift with the rpms above 3000 the engine stays at 3000 for 8-10 seconds. Also according to my scan tool, the tach is off by at least a 1000 rpm and it has low idle air counts and slowly decreases. I've put an upper intake gasket, crankshaft sensor, PCV valve, and an idle air control solenoid from a dealer in. But the vehicle idles good one day but not the next.Any help with this would be greatly appreciated. Thanks.

check ur throttle position sensor and ur map sensor.

I have already reset the TPS and it has no drops in the wave form. The MAF sensor has been cleaned once but didn't help so I tried a new one and it made no difference.