Transmission shifts fine 1st gear to 2nd gear. When it goes to 3rd at around 30mph it just free revs. If I leave it in 2, it will stay in 2. If I get going to 40-45 down hill still no 3rd or overdrive. Overdrive light is not flashing. Seems like no overdrive either. Is it time for a rebuild Or is there way to check to see if it would be a shift solenoid? I assume it shifts as it basically doesn't grab 3rd. Thanks.

Transmission fluid is full and clean.