Saturn or Caprice?

[MBCaprice]

Hello everyone, I have a sticky situation....For my birthday my mom and pop got me a 95 Saturn SL....Body was in mint condition but ran like shit at first. I had a V8 1989 Caprice Classic before this ....it looked like shit but ran like a charm...It was very reliable too might I add.
Well, after changing the transmission fluid in the saturn the gears seemed to stick better and the gears were a lot smoother when car was shifting. We also got new spark plugs and cleaned out the intake and throttle body. The only problem now is that when I back up or I am stopped with the air conditioner on it makes this horrid screetching noise which also seems to vibrate the car into mini convulsions. Also, do low RPM numbers at stop lights or stop signs (reading below 600rpm) indicate tranny problems in the future?
I do not know the previos owner or how they drove the car...and I am leary that changing the transmission fluid can actually cure all of its alements. Also, now and again...but not consistantly the tran. seems to sometimes skip in higher gears...like when going up a steep steep hill...It is not very consitant though...most of the time it seems to stick... Is it all in my head that this is not such a good birhday gift? Should I resort back to old faithful?