My truck was kicking out of overdrive on the slightest hills. I checked the fluid and it was 1 1/2qts low. I topped it off and the fluid inside seemed ok. The fluid seemed to fix that problem but now the truck shifts to neutral when i'm driving. I'll just be going down the road and into neutral it goes. Once it stayed in neutral for about a min. the other time it shifted right back into drive. Is it time for a rebuild, or does something need adjusted?