Donerighthandyman

Ok I'm new here so feel free to criticize. I have a 96 Grand Cherokee 5.2L. with a glass pack and cold air intake if it matters. It started studdering upon acceleration right about 3,000 rmps at first only at 1/2 to 3/4 of throttle almost like a governor. so i replaced the plugs. Then cap and rotor. Checked all my fluids. and replaced the MAP sensor. NO CHANGE checked the codes and got a #7 misfire and a general misfire cleared the codes after replacing the parts.... also about the same time this started i got a rattle in my exhaust something is in there right after my cat.
i have put a fuel pressure gauge on it ...it idles and runs bouncing from 40-55 or 60 then after letting off the throttle it drops to 30-50 still bouncing...check the codes manually with the engine light flashing an got a 12-43-43-55 i have refferd to the book and 12 is -battery power to pcm was disconnected 43 is-misfires and the 55 is end of message code............I am new to owning a jeep but not mechanics. but im dumbfounded plz help