1994 Jeep Cherokee Jeep Cherokee Sport '94

2CarPros, I need your advice. It appears that all problems point to the differential after reading through my jeep manual and I want to know if my car was properly reassembled or if my sweet ride all these years is finally on its last leg. In September, I blew the head gasket on LSD in Chicago. My neighborhood mechanic installed a new engine and radiator. In November the catalytic converter had to be replaced. Three weeks ago, as I was stopped at a light, my car shifted into overdrive (I now know how people accidentally plow through the front of a business). I managed to maintain control and drove staight to my mechanic. Now I have a remanufactured transmission. This morning I had the emissions test done as required by Indiana and the employees gathered under the driverside and had me sign a waiver that they would not be responsible for the hissing they heard prior to the test. This noise along with the clunking from the front end since the engine was put in, is really got me questioning if my mechanic has been doing right by me. He thinks everything is OK. I know my car is old, but these problems did not exist before the engine was replaced. I've been driving less than 1,000 per month for the last three years although I have made one round trip per week to Chicago from NW Indiana (52 miles round trip) for business. These last few months have been really expensive and the car is used to care for a handicapped parent. Thanks for your time and effort on my behalf (my Dad thanks you too).