[slowmover]

Aero only good for sustained highway, in general. Trip planning means most when the vehicle has huge penalties in acceleration and braking (I.e., the shortest route is often not the best route).

OP needs to keep records. All miles and all gallons. Nothing else matters, especially not tank to tank variations. It's the average mpg that matters.

And bring the tires down to something sensible. My 8,000-lb pickup is at 55-psi F/R. Almost on top of recommendation. Braking and handling are better. As a result (and my tires go over 100k before replacement) my tires stay in better contact with the road, AND with a larger contact patch. A high center of gravity vehicle needs some sidewall "give". It also reduces the likelihood of punctures.

. Take it to a CAT Scale and weigh all four corners with full fuel, driver plus gear always present. Pretty much any LR-E Load & Pressure Table will suffice, but tire manufacturer brand and model spec is best. That number plus 5-psi is about right. Heaviest load at either axle end determines pressure for that axle.

Best shocks and new body plus suspension bushings/ ball joints are important. As is elimination of steering slop. There's more money to be had in attending this approach.

Fewer starts, fewer stop & go over a given set of destinations, and fewer steering corrections (is pretty much the recipe for a heavy personal vehicle).

All else is downhill from that (in effectiveness).

With this exception on a diesel truck: maintenance of coolant temp in cold weather. Good to see use of block heater, but an exterior mount grill cover, and an interior "winter front" which covers the heat exchangers for sub-40F temps covers all air temps down to cold. I go from two grill cover pieces to four as temps get below the need for A/C use (and overnight temps), to their removal and use of WF when temps no longer get above 40F.

I have my doubts about cold air intake for diesels in pickups (except in highest temps and under a load), but leave that to the DD/GM crowd to figure out.