Problem running

I'm new to owning an XJ. It's a 93 with 105k on it. I'm stumped on this thing. Runs great down the highway at 75mph, idles fine. But for some reason it is dying when run between 25 and 45 mph. I have replaced the TPS, CPS, Battery, New fuel pump. For some reason when I start it sometimes the fuel pump don't kick on, wait a few min and it starts again. Sometimes it runs hours at a time others a few min. I'm baffled, could it be the computer? Let me know what you guys think.

anyone?

fuel pump ballast resistor?

Possibly also the fuel pump relay. I'd also look carefully at all the engine wiring, and make sure something isn't loose, or defective. 93 engine wiring harnesses seem to have had some issues with internal splices, though when my stepson's and others that have come up here had those problems they usually set a code.

One of the indications of a bad splice (or other resistive fault in wiring and connectors) is if the vehicle runs worse right after being parked hot. Have you noticed any difference in when the problems arise, or is it completely unpredictable?