1989 Jaquar XJS 12Cyclinder

73,000 miles
Car will not excelerate and it cuts off when it reaches operating temperture. The fuel pressure is too high also. I've changed several parts, the engine computer, fuel pressure regulators, throttle position switch, spark plugs and wires, rotor button, throttle switch and it still doing the same thing. What do I do to correct this problem? I will greatly appreciate some answers I have tried everything.