Well I ghetto fabbed up a way to make the Accel TB for earlier tpi cars to work on my 89 firebird. I took her out for a spin on the highway and floored it going onto the interstate. At about 5000 RPMS, the tach kinda floated and the engine hiccuped, so i shifted not wanting to jack up my engine. Well when I shifted (it was pretty snappy with the Raptor rebuild kit hehehe), i heard a loud thump come from the rear of the car. I took it easy until i got home and now I am here posting it about it.

1. Why is my car doing that funny floating at 5000 rpms?
2. Why is my car making that thump sound?

my rear use to make a thump when it went 2 chirp a gear but wasnt able to spin the wheels

well that accounts for the thump sound

Might also be the rear motor mount has a problem. Another posibility is you ran over something while shifting.

Do you still have a rubber tranny mount??? If so, check it out. I replaced mine 3x's after I bought the 86 in 95. One was on the stock tranny..no shift kit. The 2nd and 3rd was with shift kit. And it didnt take long. I got a EnergySusp Poly mount (they have an internal interlock) and its been in there through 4 trannys and 2 motors since 1997. Hands down the best and longest lasting investment I ever made. The thump occured during the shift and it was felt/heard in the mid floor pan area. Part # for that mount is 3.1108......most likely your issue. It can also casue shifting issues due to the tranny case floating under torque.

well i am replacing the rear end with a 4th gen one soon....anybody for the floating dilema?

isnt doing the floating thingie now....guess its ok..in fact the tires chirped tonight going from 2nd to 3rd