Just bought a 92 xjs v-12 5.3 over the winter that has sat for awhile. The problem I am having is that within a few minutes of running the car does not want to rev up past 3500 RPM then a few miles of slow driving it will only go up to 1500-1700 rpms with the throttle floored. The rpms will peak about 1700 drop to idle and then start to rev back up again. If I let the car sit and cool down it seems like I will have power for a little bit before failing again. I have done an electrical tune-up of plugs, wires, cap, rotor arm, and both ignition coils. anyone out there have any good ideas of where to start or how to do different test so I am not just blindly changing parts? Also, car starts, idles, restarts, and everything it should first time and every time no mater the temperature and never stalls out. If you guys need more information please let me know. There are too many nice days not to cruise with the top down! Please help.

Thanks, Josh