Transmission
I have a 2002 Chevy Avalanche with a 4L60E transmission. Driving around town on surface streets there’s no problem. But when I get on the interstate and drive 10+ minutes at 60 plus MPH it then shifts hard from 1-2 when I exit. I’ve discovered that when I turn the engine off, even for just a few seconds, it shifts smoothly again.This makes me think it's an electronic or sensor issue instead something mechanical. Thoughts?