Just be sure its the pump and not the box before you start replacing parts.
If does turn out to be the box and you are planning on building your jeep up in the future, that would be a good oppourtunity to upgrade the box.
Their are bigger, stronger dodge boxes that will bolt right in to a 98. If you get to that point, come and ask again and some of the guys here who have done the upgrade can explain further.
good luck
oh, and if it turns out to be the pump, I have a stock one off of my 03 4 litre because I upgraded. You'd have to find out if it swaps, I know the boxes are different, but dont know about the pumps. Wouldnt want more then 25$ for it.