Sometimes, even from the factory the valves can be out of spec. I am not saying this is a contributing factor with your truck but it could be part of it.
Another item to consider is your rolling resistance with the bigger tires...mentioned...air them up.
I skimmed through the posts so if this was mentioned, whoops...and check the brakes/rotors. One or all could be dragging ever so slightly to also contribute to your slightly lower mpg.
Alignment? Tire wear good and even?

Try SW3 at least.

Miles City...been there a few times.

Valve adjustment is next for my truck. However, I do have almost 160,000 miles and never did them.
Another thing that is overlooked...tighten all the intercooler and turbo clamps...I use a 7/16" deep socket. I think 10 mm will work too.

 

The other item I did see mentioned was your stock transmission.. My stock transmission was probably my biggest loss in getting power to the ground. Felt like a worn clutch slipping every time I would try to drive away. The convertor was horrible.. These are not cheap to make bullet proof but if you have any reputable transmission shops in your area you may want to look into making some repairs to the tranny.. TQ convertor, flexplate.. If any of the known mfrs are in your area reach out to one of them. Was the best modification made to my truck. Makes it drive completely different.

 

An interesting note:
I am running BFGs All Terrains load range "E". If I air them up over 70 psi, they wear out the center of the tire. My brother has run the D range (identical trucks) and they wear out the sides but, he kept them at 65 psi. The D range tires are rated for the same weight, but have one less ply in the sidewall I believe. They weigh 3 lbs less each and my brother says when he used to run the D range they would last 10,000 miles more than the E range. When looking at Tirerack.com website it says the D range are not rated for severe snow which makes me wonder if the compound in these tires is harder.

I will be trying the D range next time. I will be lucky to get 35,000 miles from the current set.

JP-4.5; My transmission is a manual 6 speed.

Alignment getting done today.

New brakes and slotted/dimpled rotors from brake performance yesterday.

Checked valve adjustment about 10,000 miles ago. All were good.

What is recommended for a synthetic gear oil for the front and rear diffs?

 

DON'T DO IT!

I've run the D range in both 285/70 and 315/70...the truck wallowed all over the road like a 1978 Coupe DeVille! Not only was handling seriously compromised, but they only lived 30K before I was down to the wear bars. You might consider the Bridgestone Revo 2 AT or Firestone Destination AT if you're looking for a long-life A/T tire. I've got over 23K on my Firestones and they're not even half way to the wear mark yet. Not only that, but they have much better road manners than the BFG, and handle ice a WHOLE lot better.

 

I've come across this more than once. Two tires highly rated on CTD and hauler forums are the MICHELIN AT/2 and the BRIDGESTONE Duravis 700. They'll both wear like iron, and no compromise on capacity.

.

 

If you have a wreck and you used the wrong rated tires can give your insurance company a reason to lower your coverage.

 

keep boost under 10lbs,rpms under 2000,tire pressure at max and rotate often and if u have a jr, sw3. pretty simple. sinse u live were u live tho, u might want to look into a overdrive unit so u can cruise at much higher speeds.(didnt read all posts so srry if someone already mentioned it)

 

Toe in was off by about 1.5 * total. Maybe this will help.

I will keep those tire brands in mind next time.

Will change differential fluids today. Thinking of using Royal Purple.

 

Since we are discussing MPG's- and this directly correlates to Rpm's.... Why would dodge build my truck with a Rear end ratio that puts 60 mph at 1950 Rpm? For me to even do the speed limit around town on the tollways, I have to run 2150 to reach 65 mph.... at 65 averaged over 400 miles, I got 18.47 mpg.

 

Because they built it to pull 20K pounds of trailer, and you can't do that safely, reliably, or easily with a set of 2.42s in the rear end.

 

I understand that and agree. I would just like one more gear while running empty down the road. The option fir a hi/ lo axle would be great. My 1970 single axle dumptruck came with one. Lo is for pulling 6 cubic yards and full size tractor down the road, and hi was great fir getting back home when the job is done.

 

You can do it with 2.42's if you have the right trans. with lots of gears. I wish my 48re had a few more.

 

I've caught myself reaching for 7th gear more than a few times so I know exactly what you're talking about. I agree that a dual-ratio axle would be great, but the closest we can get to that is adding an underdrive kit, and there are concerns of weakness even when not engaging the underdrive unit.

True, but a Roadmaster 18speed just won't fit with my transfer case

 

Wind speed makes all the difference. Drag is increased exponentially as wind speed increases. A head or cross wind will kill mileage. I drive the exact same route of about 400 miles at exactly the same speed. Mileage can vary as much as 3.5 mpg.

 

I live on the prairies and windspeed can change boost by 5 psi quite easily. I try to drive 65 and have a lot of Eco mods. They help a little but speed and acceleration rate are the biggest factors.