does anyone know why my 94 camaro 3.4 automatic tranny shifts in and out of overdrive at about 60 and higher, the speedo goes up when i let off the gas when i step into it the speedo goes down i just put a brand new tranny in it and it still does the same thing when i turn on the cruise it surges and then kicks off.

 

I'm not an expert by any means but my car has the same problem which even caused the check engine light to come on with a "trans slip" code. The problem is not the trans, it is the torque converter. If I understand correctly, there is a solenoid that controls whether or not the torque converter is engaged. When the solenoid craps out, the converter clutch continuously engages and disengages at highways speeds, thus the change in RPMs. Hopefully someone more informed than me can elaborate on this.