1999 montana transmission hard shift into overdrive

I just got a 1999 montana with 92k miles. The AT SHIFTS hard when you pass then shifts back into overdrive hard. Previous owner had fluid changed at dealership at 30k, & 60k miles. any help?

Is there a hitch on it, was it used to tow? First things first, get a filter and fluid change. Sounds like its the torque converter unlocking and locking hard, maybe its low on fluid right now?

Thanks, there is no hitch. The fluid level is good. I'll change the fluid and filter. Has anyone had success with additives to fluid?

I have same pro. at 11k. I rebuilded my transmission, because the fourth gear wear out. You lost your fourth gear, so no overdrive.

I have the same problem with my 2000 montana.hardshifting but not all the time. some one told me It could be over filled fluid. so I check, yes it is half a liter over, so I'll try to remove some of it.

The 4T60-E has a very shallow tranny pan it is good advise to have it over-filled by a quart,,,,under certain driving conditions,,,the trans will
"starve" for oil,,, OK,,,Under high load conditions,,,the line pressure will
rise to protect the transmission from burning out,,this is done by the PWM in the trans,,,this may be adjusted to the heavy side causing this,,
or may not be working properly,,,sometimes adding a bottle of LUB-GUARD,,,synthetic additive will help!!