IIRC your car has a pretty significant amount of work/mods. I also believe you had a QH w Dalke tune. I've read a lot about the batteries failing or the QH otherwise losing the tune. The sudden on off nature of the start of your problem sounds like that is a good possibility. Might want to try reloading, or at least verifying that it hasn't defaulted to some sort of base tune (like back to the OEM, but is mechanically close enough for no load running).
Adam