Slipping out of overdrive

Trying to diagnose my transmission problem(last gear slips) how do you pull the tcu code from the diagnostic terminal with a multimeter? When my car is warm and cruising at 65 mph it slips out of overdrive and feels like I hit a cow or something. I know it is overdrive because I will push the overdrive button and it will not do anything. Usually when you push the button it goes out of overdrive and gears down. The computer is hooked it up too, give the code p1750 which I am told is generic. That code is transmission control system solenoid assembly.$908.00 from the dealer! I am trying to determine what the problem actually is and thought I could use a multimeter to find it? Please advise.
Thanks, Shawn