Lil Dog

Good injectors might help with mileage, not slobbering 370s, but some clean low stage injectors might help. Timing is good at the 16° range from what I know.

Cold air in is never a bad thing and as said, lower EGTS help with lower water temps and overall performance. I have found that the limit for the truck is the cooling system. Having the power to pull hard gets hampered by the ability to cool it. Long hard pulls even at only 80% of my power would get the fan into full engagement and we don't live in hot climates. Your water/meth setup would be a great benefit here. I say NO to propane, always have. Too much found that the fuel causes pre-ignition and possible head gasket issues.

Gearing, lower isn't better for towing. The engine is more efficient in the 1800-2200 rpm band especially when under load. Cooling is more effective and the engines highest BSFC is in that band. Knowing this, a larger exhaust housing on the turbo might clobber all of these issues at once with lower EGT, better flow at this speed range.

Making a towing truck is a totally different objective than a racing truck so picking the parts seems backwards to most mileage threads.

Also synthetic oil is great, but not necessarily a mileage gain. Most known friction losses are less than 10% of the entire drive train excluding the automatic/manual transmission. Changing from conventional oil to synthetic oils is usually only about a 1-2% change in frictional losses at the most. So you would realize less than 1% increase in friction loss across the entire drive train. Air pressure in your tires is up to 10x that for better mileage.

9812vram

My truck tops out at 160km/hr or 100mph - I have 3.54 gears. Defueling is evident at about 2000rpm though.

The 18-2200rpm range for fuel mileage definitely does not work on my truck - empty or loaded. 54mph at 1500rpm is my on-highway sweet spot. I average 20-21mpg at these rpm and less as the rpm increases. Unless if I travel a ton of gravel at 70km/hr (empty) tq manually locked at 1100rpm - then I can hit mid 20's without trying. And why not? The engine's just idling along.

EGT's are warm at 1500rpm loaded, but the mileage is better without question. As it should be: peak torque is right around that 1500rpm.

I have a printout from Cummins for the 175hp 5.9 12 valve and it shows the lowest BSFC at 1600rpm - this is under load. That means it's making it's most efficient power at 1600rpm. Certainly fits with how my truck reacts....

These are low rpm 6 cyl diesel's. They like low rpms and they don't mind lugging - but if you push them too hard, efficiency in relation to RPM changes location, meaning a souped up truck pulling more than the truck's rated for may be more efficient in the higher rpm's for the given load.
It depends sooooo much on what modifications have been done....

cozzo1000

Verify your tires are properly inflated (trailer tires, too) and a good, straight alignment doesn't hurt either.

winkdemon

thanks guys , the truck has syn oils in it other then the engine , as thats what i run in diffs and tranys anyways , engine just good old dyno, i am going to put a set of 50hp ddps in the truck as i have set.