when im driving 50 mph + and let off the gas it drops down to 1k RPM then raises back up to 1500rpm until i cometo a complete stop but idles just fine!!! wtf could be the problem?? i have a

1986 Iroc Z28

5.0L TPI Air Foil Edlebrock Headers Magnaflow Cat 80 Series Flowmaster 3 inch pipes. 1 outlet sounds deeper... took off all AC, Heating Parts and Smog ****

700R4 With a 3,000 Stall Art Car, Reverse Manual Valve Body Ratchet Shift B&M Megashifter

posi rear end 3.89 gears

Einghbach Lowering Springs

i have APC racing bucket seats installed

Blackout Taillights

 

First thought that comes to mind is just simply your downshifting. But it might be the IAC.

 

whats IAC????

 

Just as Im re-reading your post Im now thinking it is not your IAC. But anyway IAC stands for; Idle Air Control. It is a motor operated valve. When the car is idling the blades are closed, depending of conditions that the ECM sees fit, it will open or close the IAC, to ensure a smooth idle. Are you positive it is not the tranny just downshifting, you are letting off gas and allowing car to slow down. In my experience with a good 700r4 they are smooth opperating and the downshift is not too apparent if your not anticipating it.

 

Oh wait hold on I just read all of the mods you have done. Your 3000 stall sounds a bit much for a stock cammed 5.0 motor. I have a feeling that your stall is too high.