[Big Dave]

Excellent work! You've pretty much thrown the kitchen sink at it and are getting better than double the stock MPG.

This vehicle shows that to get the really big numbers you have to do both aero and mechanical mods.

How much trailer towing do you do? Most people do a lot less than they think. Changing axles is going to get to be a pain going forward. I'd just run in the lower gears when towing than to change axles.

Short of changing to a diesel engine (a 6.5 NA fits a B-Body) or converting the CNG and jacking up your compression sky-high, I really don't see much in the way of big improvements to MPG left.