I'm a first timer here, and wondering if anybody could help me out a bit.

I have a 2000 SE with about 123,000 miles. I've only owned for about 1 year. And about a month ago my car started jerking really bad when I shift into DRIVE or REVERSE.
Also, when I am accelerating, around 35-55mph my car shakes really bad. I had a local mechanic check it out ( didn't have time myself ). He mentioned my Rear Motor Mount had gone bad, but I can't trust him because I also had an exhaust leak, and he said it was my Cat, when I finally got around to checking it out, I found out my cat is fine and the flex pipe after the down pipe is leaking. so I can't trust what he said.
And by the way, There is a lot of engine movement when I push the car back and forth, and the shaking is in the steering wheel and dash.

Thank You, ahead of time.
SCHU E

It sounds like a motor mount to me. I don't see a need to be so skeptical with this mechanic, he would have probably found the actual exhaust leak, at least he knew it was an exhaust leak and it can be deceiving sometimes where it is coming from. I'd cut him some slack and give him a chance