Transmission problem

one day about 3 weeks ago, i took my 97 Mitsubishihi Galant to get an oil change, when I got it back they said the transmission was slipping. When I drove off it was slipping. This never happened before. The problem seemed somewhat intermittent. Last Friday tI was driving around 60 is and the overdrive went out on my car, setting off check engine light. The car has a overdrive switch when disengaged runs fine in all gears in that range, when pushing buton into OD the transmission slips in and out of gear. Also I found this on another galant which I have the same problems

"replaced brakes twice replaced rotors once brakes still pulsating, horn was replaced, transmissing slams into gear" I am wondering if these are related together or model related :hi:

  patrick1053