[Fat Charlie]

I wasn't saying that increasing compression would reduce economy, I said that doing anything to your engine (other than making sure it's running properly) before everything downstream of the engine is done is going about things backwards. It looks like we agree on that if you're looking at a transmission swap before engine work.

Every little bit counts, yes, but sometimes you spend more energy chasing that little bit than you get back. Good instrumentation, airing up the tires, adding some appropriately placed coroplast and developing an appropriate driving style are going to get you 90-95% of the rig's available economy. Everything past that is going to be for the personal satisfaction of running up the score, rather than actual fuel savings. Big work trucks are only economy disasters if you aren't using them for work- you can do many things to get them a bit higher mpg, but it's not worth going overboard for.

Your alternator can probably already produce more electricity than your truck uses. Adding weight and aero drag for a solar system won't eliminate the weight of the alternator, but it might slightly reduce the amount of drag the alternator produces. If you think it's enough of an offset, or if it's simply something you want to do, go for it. If the truck is going to spend a lot of time stationary and you want electricity without running the engine, carrying panels and setting them up in place is probably a better move.