So I've been having a fuel delivery issue ever since I started driving my Cherokee. It's a 96 4.0 5spd. It runs fine untill about half throttle, then it just flattens out and doesn't have more power. Sometimes it bogs. I put on a pressure gauge and it was right where it should be at 50psi. Thinking fuel wasn't the issue I changed the rear o2, no change, checked the TPS and MAP and they were fine. I pulled the hood off and hooked the guage up again and drove it around and at more than half throttle the pressure would drop, sometimes down to zero at WOT. So I changed out the pump and regulator and nothing really changed. I bought a second pump and just installed it today and still nothing has changed. Pressure still drops. I checked for kinked fuel lines and they were fine. I also swapped in another set of injectors just to rule those out. I also unplugged the pump and ran it straight to a battery and still same issue. I'm stumped and done know what else to do. Any ideas?