94 Jeep Grand Cherokee Limited not shifting in any gears

SOURCE: 2000 jeep grand cherokee limited starts in 3rd gear

oil pressure problem should be checked independently of other problems...Use a good accurate mechanical gauge to check. If pressure is good (no less than 15psi at idle hot (I prefer to see at least 20) check dash grounding, block ground and if OK, change sending unit. Dash and body ground can influence operation of shift and body control modules so indirectly your problem may or may not be related, depending upon what you find while testing. And it could turn out to be a defective module! They are expensive and just plugging new ones in may work, but then again, it might not. I might be totally incorrect on this...that's the value of actually being there instead of doing this by "remote control".
If you read the numerous posts pertaining to all vehicles, you will see that you are not alone with electrical problems...As long as the engineers who design this stuff, keep using "modules" to replace ordinary simple and reliable systems, we will continue to have these problems. Do some testing and I'm sure you will find a solution! (I'm still waiting for someone to make a program for a PC that will give a complete readout of every system in a vehicle, including exact faults instead of general system "suggestions")
Good luck

SOURCE: fault code P0720

code po720 is the output speed sensor malfunction

SOURCE: 94 jeep grand cherokee will not shift into overdrive

My 97 Jeep Grand Cherokee was doing the same thing. I changed the TPS ( Throttle Position Sensor) Now it is great goes into overdrive fine. It is really easy to change.

SOURCE: 2005 Jeep Grand Cherokee Shifting Problems

Check the Trans fluid level with it running and at operating temperature. Jeep NAG1 transmissions are known to have the input electric seal leak trans fluid. Not an exspensive fix add Mopar ATF4 and then relace the guild seal.