engine problem ?

I have a 1995 tracker , it just started to vibrate really bad when i'am up to about 35 mph and over and if i rev it up , thought it just needed new plugs . replaced them and it's still doing it . almost sounds like something got shook lose but can't find anything . i hope the engine isn't shot . does anyone know what it could be ? It has about 137 K on it

If the engine were bad you would probably hear bearing noises, such as a rythmic clunking that matched the engine speed.

Vibration usually indicates something out of balance such as a bad U-joint, warped flywheel/clutch/pressure plate, or a harmonic balancer. If it vibrates while rolling it could be a bent or out of balance wheel, or a warped brake drum/rotor.

Please provide more details. Does it vibrate when standing still, or only when rolling? Is it making noise, and what kind?