Jack each side up from the Lower control arm to unload the balljoints. Check for play in them. Also, grab the tire at 3:00 and 9:00 and see if there's any play.
You said you checked your u-joints. Driveshaft u-joints or axle u-joints? You might have a late model 97 instead of a 98 if you have u-joints in the front axle.
Good luck and report back to us with any findings
I dont know if you have a carrier bearing or not, but I would check there as well. Some early model 98's had carrier bearings.