Re: 98 jeep grand Cherokee vibration
Its hard to say without feeling the freequency... if its a really fast vibration I would lean towards driveshaft balance or ujoint, if its a bit slower, tire balance... Inspect your tires for any obvious damage or wear.
If your tires are really tired I would start there, even if it doesnt fix it it never hurts to have good tires if you needed them, much better than replacing ujoints and other things for no reason.
2005 Jeep Grand Cherokee - Gone but not forgotten!