Just got done reading this thread (4T65E Hard Shift-Solution) and it seems to be a great fix for our exact issue. I'm still going to get a complete rebuild because I have so many miles on my transmission, but I like the idea he gives about putting the cooler on and bypassing the radiator to keep tranny oil temps down. I will probably do this on mine after the build. Since you've only got 100,000 miles, you might want to try this before shelling out a bunch of money. Looks pretty simple and cheap.
