engine vibrating ?

It could be the motor mounts...It could also be something anywhere in the driveline. You would be amazed at the amount of vibration that can be misdiagnosed as an engine or tranny problem that ends up being something in the rear axle!!!!

Check how much the motor deflects when someone snaps the throttle while you are looking at the engine.

It could be that you are loosing compression in the engine or something else internal is going on.

Check the flywheel/flexpalte for cracks and check your tranny level

sounds like a broken motor mount. theres a easy way to find out. start your truck, hold your foot on the brake and push the gas, the motor should raise way up, if the mount is broken, you know,(power blocking)

I would suggest a new set of motor and transmission mounts. They are probably worn out.

Check your engine mounts, if thats not the problem, then you probably have a worn engine with uneven compression.

It might be the engine mounts, but it could also be the spark plugs wires that need to be replaced.

take it to a mechanic =]

it sounds like a motor mount its usually the drivers side

maybe you have some misfires. you should check for that first. A scan would also help.