While out of town, my wife called me to tell me that when she came to a stop at a light, the oil pressure dropped to zero. When I returned home, I checked and found that there was plenty of oil, in fact there was too much because she had added another quart. I started the Jeep and when I pressed the gas peddle the oil pressure came up, but dropped when I removed my foot. Whet do you think?

Sounds like you might have a bad oil pressure sending unit, however I previously worked at a chrysler garage, and from 99-01 the jeep 4.0 liter engines were notorious for cracked cylinder heads which allowed the coolant to mix with the engine oil, if your not using any coolant this probably isnt your problem however if you have been adding coolant to you jeep for awhile its bad news because the coolant mixing with your oil has worn out the camshaft bearings causing excessive oil clearances which shows up when your engine is hot and the engine is unable to maintain oil pressure because if the oil clearances being so great.....