Engine low power

I have a 1990 Jeep Cherokee Laredo 4x4 Mileage:112,000 It has difficulty starting every time, sometimes taking up 1 min of continued cranking before it finally starts at times. While it is running cold it idles just fine, but once it gets warmed up it hesitates, putters (sounds as if the spark plugs are misfiring but the spark plugs are just fine) and after a few min dies out. While engine is cold it pretty6 much revs fine and again once a little warm it will ideal but start to die out eveytime I gas it a little gas I have checked the fuel filter and it is fine as well. Was told to check the fuel pressure regulator but don't know where that is located, could someone please tell me where to look for it and how to check it to see if it is working properly. I know it should be at 31PSI, just don't know where to find it. From what I can gather I am figuring it to be some sort of fuel system problem. The filter is working just fine, can blow straight through it. :

Old feel pump was reading 30psi so I replaced it with a new one and it is reading the same. I’ve done plugs wires distributor coil air control valve throttle positioning sensor. What my vehicle is doing is from a stop sign to a go it chugs and jerks then once you start up a hill it loses power and you have to drive up the hill in reverse you put it in four-wheel-drive it dies once you put it in drive but if you put it in four-wheel-drive and put it in reverse it works fine. Any ideas?

It doesn’t pop up any codes when I do the key thing. I don’t have a maintenance light on. Catalytic converter’s gone. My stereo started flashing off and on when I did the key thing but nothing on the dash maybe somebody messed up putting in the stereo I haven’t looked at that? But I don’t think that would have anything to do with my issue. And I forgot to say earlier I did I feel filter too. And thank you for your time in answers.

And I forgot to say I only have 30 pounds of pressure with it idling when I give it gas it goes down to 28. If I undo my hoes on my pressure regulator it goes up 5 pounds. So the regulator is telling me it’s good.