You sound pumped . I was beginning to think this one would go unsolved! If the ballast was the only (electrical) part changed you might swap the old one back in for a 5 minute test just to pin things down even further & it'd be a piece of cake to do. I'd suggest a 10 micron high flow filter between the mech pump/carb & a 100 micron high flow filter ahead of the electric pump if an electric pump is being used. Definitely flush the tank/lines