Below is what your oil pressure sending unit looks like but this price may be a little high. It's best to take your old one in to match it up because they come in different lengths and can sell you the wrong one.
Can't imagine your oil pressure actually dropping to zero or your engine would be making a bunch of racket and may come apart. You could probably remove your valve cover cap while running and see if it's spitting oil/flowing.
I'd be replacing your sending unit first since dropping the pan to replace the oil pump is a pain. Also agree on putting a new rear seal in it and don't buy the cheapest oil pump if you end up doing this. Use only a Mopar or Felpro pan gasket and rear seal. Hopefully you won't have to go this route and good luck!
BTW, with a 4" lift you may not have as much problem as I did in getting the pan out on my 96 4.0. Had to remove the top shock nuts, the sway bar link nuts on the bottom and finally the track bar bolt to get the axle to drop down far enough to get the pan out.