I have no overheating issues with my 2000 Auto. Tranny temp gage(Autometer) always sits about 80 degrees over ambient.
I have 141k on my stock tranny and no issues. I have done some small internal mods to help pressure and flow along with firming up the shift points, but less than $100 spent.
If it drives well on the test drive, with some hard launch/freeway entrance ramp runs I would not worry about it.
The one big issue with the 99 Autos was the torque converters. When they started coming apart, they sound like marbles rattling in a coffee can. Once the converter starts going bad, it sends metal throughout the tranny, killing it.
