I have a automatic 1999 pontiac grand am gt. the car and drives good until it heats up. then the gears shift extremely hard. and when sitting in idle you can hear a loud winding noise coming from my transmission which has been rebuilt recently. and another strange thing is when i'm driving normally or on cruise control i can see the rpm randomly go up and back down but doesn't accelerate. and now if that isn't bad enough here about a week ago my temperature gauge will stop working when the car shifts and will randomly come back on..and if i turn the car off without the temperature gauge working its very hard to start. please help me im no mechanic ..

Check the transmission fluid level. Also check the rear differential if your car has one ( I think the 99's were still rear wheel drive) for fluid. If either of these are low, the fact that things are fine indicates that the low fluid level is causing problems. Also, the trans fluid should be a nice pink color. If it isn't then the transmission is not in good shape and should be looked at again by the rebuilder. If the fluid levels are fine, have the rebuilder check the trans again to see if he missed something.

The issue with the temp gauge is entirely separate except if you mean that the car begins to heat up when the shifting problems are occurring. If the temp gauge goes way up then comes down quickly regardless of how the car is being driven, the thermostat may be sticking and should be replaced. If the car is hard to drive and then starts overheating, the transmission may well be defective and causing the engine to work harder than it should.