98 k1500 4.3 manual trans high idle problem??

i have replaced the IACV, TPS, TB base gasket, intake gasket (upper and lower), checked for vacuum leaks and checked all the wiring to the sensors on the throttle body. it idles great but when i depress the clutch to shift gears (ie 1-2, 2-3, 3-4, 4-5) the RPMs either stay the same or jump up to 2000-3000 RPMs and will stay there until the truck has come to a COMPLETE stop then the RPMs will drop down to an idle. it does the same thing when i go to down shift. Its extremly annoying trying to down shift and the truck wants to do the complete opposite. also there are no check engine lights on and i hooked up the computer at work just to make sure there wernt any codes. Any ideas would help. Ive asked 4 different very reliable mechanics in my area and a few buddys that work on cars a lot and it has them stumped too. Thanks, Tony

i have replaced the IACV, TPS, TB base gasket, intake gasket (upper and lower), checked for vacuum leaks and checked all the wiring to the sensors on the throttle body. it idles great but when i depress the clutch to shift gears (ie 1-2, 2-3, 3-4, 4-5) the RPMs either stay the same or jump up to 2000-3000 RPMs and will stay there until the truck has come to a COMPLETE stop then the RPMs will drop down to an idle. it does the same thing when i go to down shift. Its extremly annoying trying to down shift and the truck wants to do the complete opposite. also there are no check engine lights on and i hooked up the computer at work just to make sure there wernt any codes. Any ideas would help. Ive asked 4 different very reliable mechanics in my area and a few buddys that work on cars a lot and it has them stumped too. Thanks, Tony

hook up a vacuum guage with long hose to monitor manifold vacuum. drive vehicle and see what happens.

on acceleration vacuum will drop. when down shifting vacuum will go to the max.

could be hi vacuum is sucking the fuel out of the TBI.

Just a shot in the dark but is your throttle linkage sticking? If you "goose" it while clutching does it still do that? Is there a adjustment on the throttle-stop that has been turned? fuel pressure reg?? hope this helps and gives you some fresh ideas.