Th400's and 80Es are known to have harsh reverse engagement. As stated its probably a high idle issue. A couple hundred rpm difference could be a difference of 100psi line pressure to 300 psi line pressure (this is normal and intentional for reverse in an 80E).

 

I have another similiar issue...the trans is very difficult to turn in reverse, by hand or backing up. So much so that the truck has a hard time keeping a steady idle if I back up, as soon as I shift to neutral or drive its fine.

 

is it under warranty?

 

mine does it too... i have a stock converter though. im not worried about it.. im worried how long it will last behind 800 hp though

 

When you try to turn the output it will turn with more resistance in one direction and this is reverse. So this is normal. In most cases with a stall your idle will have to be increased for reverse and its pretty common complaint that the engine wants do die. I have seen this complaint many times with a 60 so IMO you have the same thing going on with your 80. Vince

 

Ok...I never noticed it with my 60s or my built 80e with the same current torque converter, just this rebuilt 80e.

 

I don't have the harsh engagement, but on a cold start if I don't wait for the rpms to come down shifting into drive the rpms will transiently shoot up to like 1300.

 

Is there any harshness when shifting into drive under the same conditions as shifting from park to reverse?

 

Nope. Its a firm apply, but not nearly as violent. I let blake and mitch hear it apply to reverse at the meet and both of them were kind of shocked it was so violent.