Dr. Dyno said:
As Eagle said, Hesco can't be held liable if you only bought the stroker kit from them while you had a local shop do the engine build-up. That applies even if the engine's done only 20 miles, never mind 20k.
In any case it sounds like your problem is fuel delivery related, not engine related. The combination of gas coming from the exhaust with a shaking engine suggests that the engine is being flooded with too much fuel. The possibilities are bad fuel pressure regulator (check fuel pressure at injector rail) or injectors that are stuck open.