I drive a 92 4.3 GMC Jimmy, and the other night, I hit a pot hole, and lost control and went thru a ditch.

After I got out of the field and back onto the road, my engine sounded funny and was causing a vibration that it hasn't before. I can see the muffler shaking at the end, and the steering wheel shakes, and it isn't an alignment problem, because it does it in park. I put the hood up and hit the accelerator, and the engine shakes side to side not violently, but alot more than it did before. It also feels liek it doesn't accelorate as hard, and my gas milage is someone worse.
I believe either a cylinder isn't firing, or I broke an engine mount or it's loose, or, if someone knows, tell me what the problem is!
And can someone PLEASE tell me where the motor mounts are so I can check them?
Thanx for anyone that is of any help!!!