I have a bone stock Avalanche 3/4 ton with a intermittent cold shift problem.

If the trucks sits for a few days and on cold start it won't engage reverse gear immediately. I can put it in reverse and the usual clunk into gear doesn't happen and actually feels like the truck is in neutral. But if I leave engaged and give it some gas the truck slowly starts to roll backwards.

It feels like the trans has no pressure and it slowly starts to build up and finally starts moving. If I shift into foward it seems to go OK. Again, this is only when the truck has sat for a couple of days or more and doesn't always happen.

Maintenance on the truck is up to date and tranny fluid is clean and at the proper level.

Any ideas? Otherwise runs/shifts fine once it gets going.

Looming problem?

sounds like the reverse servo may need a new oring..you would loose overdrive if their were any internal dammage..also letting the truck warm up before driving it should help..

Do you only back up from where its parked usually? I own a transmission repair business and what your describing is what is caused normally by "convertor drain back", oil seeps slowly from tq convertor thru the pump gears and when you go to move it has to re-prime the tq convertor. How many miles?

Truck is parked in the garage, so startup and then reverse out. I never back in so always engage reverse first.

60K miles on a 2005 (the truck is for towing the boat and winter driving duty only) hence the low miles.

not doubting artic,monitor the trans dip stick when sitting..if it creeps to a higher level then i would say he is rite!

Had a similar issue on mine when it was brand new a few years ago. Dealer replaced valve body and TC which fixed it IIRC.

My 12v. Dodge trans has tq conv seep also.

Dodges torqueflights have always been famous for this, a Transgo shift kit with a re-designed manual valve will really help with this, in stock form there is no convertor flow at idle in park so it doesn't start to refill untill you go to move, with the S/K it will flow thru as soon as you start it and you will probably never even notice the problem again, Smitty

That is good advice. If truck sits for long periods of time and you keep having this problem you can choose to live with it and it will most likely never hurt anything, just give it a few minutes to re-prime, Smitty