How have you established the tank is empty? You could have heaps left.
What you now need to do is fill up and figure out the actual consumption, not some random guess based on a 20yr old fuel gauge..
How did you lap the valves, and why?
Do a leak down test or at least out air into the cylinders, I reckon you have valves not Sealing correctly. That's my current guess anyway
did you tell them it is pretty important to get it done quick cos plenty of people on the internet are waiting for turbo noises and skids? that should speed them up
Are you saying it was missing with stock coils so you put in yellow jackets and it fixed it, now it is missing again?
I'm that case it is definetily the coil packs.
If you have 20, 000 you can put in the bin and it won't effect you do it.
I certainly wouldn't be counting on any warranty situation with builds like that.