Fuel pump or Regulator???

[SPROVER]

Last week the Disco started to develop a bad flatspot and lacked power through the rev range when running on petrol.Some specs first.V8 3.5 injected 1993 model running gas as well.I ran out of gas so i turned it on to petrol and it just felt gutless and slower then usual:eek: It idles smooth and i have swapped AFM to check and it still does the same thing.It has new plugs and leads,new rotor and cap,coolant sensor and new fuel filter.Runs fine on gas so im assuming the ignition side of things are good.Just need to know where else i should start looking! Any help would be great.

Thanks
Chris