I bought a 1997 Grand Cherokee Laredo 4.0 I6 a few months ago and replaced the fuel pump as the old one was messed up. After I put it in it ran like a champ. Bit of a side note I had to use a TJ fuel pump because a TJ fuel cell was put in the trunk and the old tank was dropped. Recently though the jeep has had issues starting and most importantly stalls or shuts off completely while driving. Sometimes it will start right back up and others it will not come back after many tries. I tested the rail to see if it was getting enough pressure an it is. The fuel pump also sounds just as loud as the day we bought it.Does anyone have any ideas as to what it could be? My only guess is the crank shaft sensor.

Yeah, that's my guess as well.