I have a 2007 Jeep grand Cherokee with around 150,000 miles on it. I have been having a problem lately in that after turning my car off, it will not turn right back on. If I wait about 40 minutes, it will turn back on right away.

I have replaced the cam sensor, but that did not do the trick. No one has been able to tell me the exact issue, but I am beginining to think it might be the fuel pump (when i stop and get gas it fires right up).

Has anyone else had this issue?

When you say "will not turn right back on" do you mean it won't crank when you turn the ignition on or won't fire after cranking?

Seriously you can just sit there and wait 40 freakin minutes? Kudos to you for sure. If my junk dies and wouldn't fire after the second try I would have already had an ad up on CL and called for a cab to take me to the dealer to look for a new ride.

When this happens, check and see if you can get any air out of the valve on the fuel rail. If so, it is vapor locking. The under hood heat is causing the fuel in the rail to turn to vapor and it won't start until it cools enough to turn back into liquid. If you get any air out, try purging it all out then try restarting the vehicle. My wife's '05 Liberty is going through this right now.

Better suggestion would be to attach a fuel pressure gauge. If a press on the schrader valve sprays fuel all over a hot exhaust it's over.

It will crank, but not ultimately turn over. I have attached a fuel pressure gauge when it does turn over and the pressure is normal.

What engine? Any codes?

Crank? Turn over? When an engine 'cranks' it is rotating by the starter. When it 'turns over' it is doing the same thing. If you mean it cranks but won't start, you need to say that.
It does sound like a fuel pressure regulator, pump, and filter issue. You need to replace all three. But the whole assembly and drop the tank. However, nothing replaces a good guage in the right hands...best to be sure before you spend time and money..but is certainly a good bet with that many miles.