Trans experts help please, 97 Montana wont go till warm
 

Its a Lounge post cause its not a Bonneville, but the trans in this thing looks like a 4t60, judging by the pan.

When cold, or after idle for a bit, the trans REFUSES to engage, if you let it idle in Park for about 10 mins, it will kick in and go like nothing wrong. shifts fine, maybe a mild whining noise from the trans and thats it.

Fluid has been changed.
Vehicle has 160k on it.

Is it circling the drain? or something I can fix easy, easy meaning I dont have to take the trans OUT. Its my sisters car, the only one.

Sounds to me like an internal pump problem..

Internal, meaning this thing has gotta come OUT to fix?

Depends on how much room you have between the side cover pan and the strut wall. You might be able to pull the pan off and check the pump. Would require the drivers side driveshaft to be removed to get the pan off. I have pics with the cover off. Complete tear down of the 4T60E. It just makes it easier to pull everything out of the transmission when it is tipped up and reinstalling. I put mine back together while in its normal sitting position. It's a PITA, but it can be done.

This could be the perfect time to persuade her (gently) to get an H-body. There isnt much room to work with under these hoods, maybe the wheel well splash shield would afford a bit more. I am not brave enough to try this on a daily driver that someone is depending on.

Sad thing is, it works PERFECT when warm, drove it myself and I wouldnt be scared to go on a trip with it, just have to let it idle for a few mins before attempting departure LOL. I feel its probably on its last legs though.

Yeah thats the main cause of "slow engagment into gear when cold"
Most cars take a bit longer in the winter due to the viscosity of the ATF, however, when it isnt sub zero and its having trouble, its done..
4T60?
3.4L?
I might be wrong here but that should be a 4T45E