P38A intermittent power loss

evening all,
my 4.6 rr has had this very intermittent fault for some time now and i cant find the cause, the engine is rebuilt with about 3k on it so far, but i did have this problem before.
it runs multipoint lpg, but the systoms exist on petrol and lpg.
basically most of the time it is very responsive off the mark, but then sometimes it feels very slugish and seems to have no response from the accelerator pedal. i had it today while towing.
sometimes just nothing happens when you press the pedal, other times a missfire.
i can turn off the car and it will reset.
so far ive had all plugs out and all are burning the right colour and uniform.
no overheating.
checked all connections.
and nothing shows up on hawkeye diagnostics.

i have a couple of ideas but would welcome other opiniums please.

no ideas anyone?

The V8 lot are probably still hung over from the weekend champers. Not had a lot of experience with the V8 but I'd be checking ...

How old are the HT leads?

How do the lambda sensor readings compare side to side? Are the fuel trims reasonable?

Is the lift pump losing a bit of vim?

Hopefully someone like @Saint.V8 will be along soon with a more informed reply. If he's not still lost in rapture up to his elbows in knackered 3.5 engines.

hi,
gonna check ht leads but they are magnacor leads, lambda readings are good and work in harmony as i can see them functioning on my lpg software, what is reasonable in terms of fuel trim values?

as for the lift pump its the same on either fuel so i guess that rules that out.
cheers