Starting point:

1996 half-ton pickup extended-cab fleetside 4wd auto & air

It's decent on gas so far, but I want 25+ mpg highway (28+ would be even better). I want to preserve sort of a medium off-road capability (nothing overly extreme, but not completely wimpy, either).

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Eventually (maybe 40-50k miles from now), I will want to lift it & put larger tires on for mainly cosmetic reasons; if I could keep 20+ mpg with tires in the 33"-37" range (haven't yet decided), I'd probably be quite happy.

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Any ideas for such a combo? I figure aluminum heads are just about mandatory, as is higher compression for thermal efficiency -- but there are different combustion chamber shapes and all sorts of other things to consider.

Anybody with real experience in this area, feel free to share your combo unless its a secret: this is going to be a slow build, with incremental gains, but I need to plan the whole thing before I get started. I don't want to open the engine, do a mod, button everything back up and then have to get another set of gaskets 6 months down the road.

Thanks for all the helpful info!