Here's a thought. Buy an older gas truck with a run-out engine. Build a =new= gas engine, as potent as you like, make sure the tranny will handle the engine, make sure you've got the gears you want. Might cost about the same as a new truck, but you now get to register it as the older model truck =and= you only have to meet that year's emissions (if needed). Hell, if I could afford it, I'd drop a late-model Duramax in my '02 and dump the DEF. :-) Yeah, I wouldn't mind an extra near-200 h.p.
Lyle