First question - how many miles are on the vehicle and transmission? Second question - when was the last transmission service; fluid and filter change? No flushing is recommended!
First thing first, check transmission temperatures
If it is higher than 95C, then most likely you have a problem with transmission cooling system or your engine cooling has some leaks causing running it very hot.
Usually high temps indicate following:
1) engine cooling system problem- air bubbles or airlock.
2) if everything is good with cooling system, check your transmission oil cooler- it gets clogged up pretty often and also indicates that some clutches or Torque converter clutch is worn out and that debris clogged oil cooler.
Reference various TSBs = B 24 13 07
"Various complaints associated with inoperative transmission controls."
Transmission Connector X8500, pin 14 is slightly pushed back causing a poor connection.
If you use DS or M modes often, wires attached to the shifter stress and break. See this thread for a video that explains what to look for and how to fix it:
6HP19 E Clutch failure / clutch failure
Problem - Clutches are responsible for helping the transfer of power from one gear to the next. They're lined with friction material that helps the clutches to grab. These wear out over time, or prematurely due to improper maintenance. Symptoms of 6HP19 clutch problems include slipping, delayed shifts, harsh shifts, failed gear engagement, and overheating.
Solution - In order to correct this common 6HP19 transmission problem, the transmission will pretty much have to be rebuilt or replaced.
6HP19 Transmission Specs
General - 6-speed automatic
Application - RWD/AWD/4WD
Variations - 6HP19A (AWD) & 6HP19X (4WD)
Production Began - 2003
Weight - 158 lbs - 169 lbs
Fluid Type - ZF Lifeguard C
Capacity - 8.9 qt