[slowmover]

If those tires are five years old, time for new.

Tires that sit, dry rot. Heat from use is NEEDED to keep them in shape. The expectation is 3-5 years tops. Mileage not a trailer tire life consideration.

As to rig aero, the truck bed needs a cover. A thin piece of plywood extending from tailgate to 1/2 the distance to the cab.

As to MPG, it’s about steady-state. Below the flow of commercial traffic. One uses mirrors to manage their getting around your rig ASAP (slowing to accomplish this when they have less than a 5-mph variance). It’s a different set of habits.

The “goal” is maximum distance from all other vehicles throughout the day while still on cruise control. No lane changes (which means sub-65 travel speed).

A cruise control set of from 62-64/mph is as high as it gets. Then, monitoring traffic. With a jam of vehicles up ahead moving more slowly than this, one backs off in speed until it clears. It will. Always does.

Same with any passing. Done when alone. Only.

The relationship between Average MPH and Average MPG is the fundamental. Use engine hours against the day’s trip length for the former.

It’s a rude awakening for those who believe a speed like the above is too slow. As a faster speed that causes one to have to pass more doesn’t result in a faster trip time, per se. The few extra minutes “saved” means MPG gets a broken jaw.

Traffic volume (road design plus other conditions) dictates travel time. Not set speed.

A few mph extra can show NO BENEFIT, only deficit. I do this all day, every day.

In short, if there’s ever a time you’re within a football fields length of someone else, you need remedial instruction. (Heard the phrase, “cant fix stupid?” That’s the guy surrounded by other vehicles).

Safety trumps MPG, but, happily, they track each other most all the way.

Along with engine hours & odo reading at day’s beginning on a note card, also set categories for braking and acceleration events. Mark each one. If you’ve slowed to get someone around you faster AND can use a downslope to regain set speed, that doesn’t count against you.

The “ideal” trip has only one each of those events. Absolute zero idle time. The trip is from when parked from overnight, until being parked for the next night. All miles & time. Not highway only.

Planned stops only. And then, only after the original first two hours at highway speed (as this is the initial warmup and lessens re-start penalty). Make the stops at locations in the same direction of travel, and with fewest number PLUS degree of steering inputs. Etc. (These details matter greatly).

On the vehicle CONFIRM perfect alignment (Ford always a problem), trailer axle alignment, and that trailer brakes & bearings are properly adjusted. Trailer tire pressure should be to sidewall maximum. Truck tires are from a CAT SCALE weigh ticket and consultation of the Load & Pressure Table of that tire ratings category. (Inside vehicle manufacturer range). Not higher or lower as that worsens handling & braking.

One is also looking for caliper drag on the tow vehicle. And, with a turbodiesel CONFIRM no CAC leaks.

Seat posture is that ZERO reach is needed to the top of the steering wheel. Arms not at full extension. Mirrors adjusted accordingly. Driver fatigue is the thing. Everyone is affected. A bad seat cushion, as example, needs remedy. Alertness throughout the day is what preserves those tenths of a mpg.

Any aero with the trailers contents is worthwhile. But, first, CONFIRM that the trailer tongue weight is more than 10% of the trailers total weight.

At the CAT SCALE, do two passes after topping fuel tank and keeping all passengers aboard:

1). Rig as hitched.
2). Truck only.

At home prior to this, find a copy of the trailer tongue bathroom scale weighing method. Numerous sources. Find the empty and loaded values. Use a carpenters level on trailer to have it dead level when weighing.

To hitch the trailer one needs it as close to level as possible. A half-bubble out is almost too far. MASTERLOCK and some others used to sell an infinitely adjustable hitch that makes trailer leveling easy for under 5k of load. I bought mine at U-Haul. It’s an Acme Screw. One uses a box wrench to raise or lower.

MPG is a question of details. If you truly want it, then one has to chase them. An alignment good enough to get down the road ISN'T the same as ideal, for example.

Just as driving more slowly isn’t enough. It’s the totality of every input the truck receives through the day. Less is more.

As an example I’ve hooked up U-Hauls largest enclosed trailer and with a combined weight in excess of 13k still seen above 18-mpg towing on two separate trips of 350-miles. On a the truck below in signature, where, with almost a quarter-million miles is just finishing its second set of tires and has had one brake job. 50/50 Town & Country miles, it was spec’d with FE in mind.

MPG is a GREAT way to chase down details. See contributor Big Dave’s many Ford posts here, and see his Fuel Economy subforum on one of the Ford enthusiast sites.

One has to have a plan. Records. Baseline numbers.