installed new rear gears now my trans slips bad in 3/4 gear?

[remaxracer45]

I went from a 350 to a 390 rear gear and now my tran shit on me. it works fine in reverse and first and second but slips really bad in 3rd and 4th. Car is in the sig was built 15K ago with all the high end internals. Help

[QC97Z]

If you're getting acceptable driving conditions in reverse, 1, and 2, but not 3 and 4, then it sounds like your rear is fine.
I'm not an automatic guy, but is your current torque converter compatible with your gear change? The reason I ask is because reverse, 1, and 2 are all on the "larger" side and they're all working fine. I'm wondering if, because 3 and 4 are "smaller" gears and will deliver less torque and more top speed, is your torque converter now mediocre because of your gear change?

Slay me, automatic guys. I'd like to know more about them anyway.

[94Z28rag]

Has nothing to do with that gear change, it's not a significant change anyways. You do need to have it retuned for the new gears, though.

It may have just been bad timing and the trans went.