in my 93 4x4 I would only get 19mpg, it had a stage II diesel converter, major pump mods, fuel pin, and pump timing adjustments. It was borderline runaway and had a fuel cut off pull cable just in case.

Also the "smoke" screw was set to roll coal by the prior owner, and I never had it reset.

I'm sure had it been adjusted a bit more conservative it would have done better