2000 Chevy Silverado Transmission shifting

I got a 2000 1500 Silverado from a family member. The truck had a bad rear differential and had been sitting for 3 years. I had to replace the fuel pump, had someone re-build the rear end and I replaced the tranny filter and flushed 16 quarts of fluid thru it.
The only way it will shift is manually. Rumbles a little in 2nd when you give it power at lower speeds.
When you kick it down in 3rd and 4th it just free wheels and won't shift. Is it a specific solenoid since it sat for 3 yrs. Or is there a fuse. Can't find one blown. Really need this truck to work.

Jeff C.