Won't shift into overdrive

2001 buick lesabre custom, 105,000 miles, 3800 v6 engine. Transmission would not shift into overdrive yesterday, we started out with a cold engine and even after it warmed up it would not shift from 3rd to overdrive. Stopped and ate breakfast ( 10 mile drive). Came out and drove home now had what sounded like a low fire whistle sound that would get higher pitched as engine rpm increased and still would not go into overdrive, got back home and had a hot smell coming from under hood(almost like a hot electrical component smell) checked tranny fluid and is normal as well as radiator fluid. Car ran fine day before. No idiot lights came on. Also transmission was rebuilt exactly 1 year ago and new radiator with tranny cooler installed at same time. We have had alot of problems with this car. Please help me out? Thanks