Here's a list of the items I have on-hand slated for install based on everyone's feedback and a few months of research to increase my Fuel Efficiency:
1- 200* thermostat from 2010-12 model Cummins (Geno's Garage)
2- AFE torque tube
3- Goerend Torque Converter- 15SS model Goerend Dodge Diesel Torque Converters
4- Goerend billet flex plate SFI approved
5- Flex-a-lite electronic fans- dual 15 inchers
6- Fitch Fuel catalyst filter https://fitchfuelcatalyst.com/auto
7- Micro Green Oil Filter MG430-9- 2 micron particulate matter (instead of 25-30 particulate matter filtering..) microGreen | Extended Performance Oil Filters
Royal Purple 5W-40 synthetic oil
Cetagreen (?) additive fuel injector cleaner
Hot Shots Diesel Extreme

Three items I am still in the hunt for are:
1- Aftermarket front air dam to cut down on the underbody resistance
2- EFIlive AutoCal and tuner for tunes
Les from Silver Bullet Tuning has not responded to my requests from last week (if you know Les, let him know I am buying this week- either from him or another tuner)
Lavon at Firepunk has been recommended, but never replied to my emails over the last few weeks... (same as above)
Ryan at Hardway Performance is next on my recommended list
3- Turbo Air Guide TAG-III 94-07 5.9L Dodge Cummins; if you see one for sale - or have an extra in your toolbox - please let me know

Which transmission fluid gets the best results?

If you have any other insights for POL or improvements, I am all ears.

Thank you for your time.

I successfully installed the Fitch Fuel Catalyst today. Results will be posted after I put a few miles under the truck.

My first drive (139 miles) with the Fitch Fuel Catalyst resulted in a 1.8 mpg increase; both town and flat highway combo.

was there any other changes to the truck besides the Fitch? You not wanting manual hubs?

The results gained from the $300 Fitch Fuel Catalyst have remained impressive.
The second tank held strong with a 1.2 mpg increase; more town driving than the first tank.
I'm interested in replacing the front hubs with manual locking hubs, but lack the money for free spin hubs.
So as of now, the Fitch Fuel Catalyst is the only big change.
The only other minor one right now is a Micro Green Oil Filter MG430-9- this filters the oil at a 2 micron particulate matter (instead of 25-30 particulate matter filtering..

I will keep the thread updated when I make the next batch of upgrades in early May:
1- 200* thermostat from 2010-12 model Cummins (Geno's Garage)
2- AFE torque tube
3- Goerend Torque Converter- 15SS model Goerend Dodge Diesel Torque Converters
4- Goerend billet flex plate SFI approved
5- Flex-a-lite electronic fans- dual 15 inchers
6- EFIlive AutoCal and tuner for tunes from one of three recommended tuners
a- Les from Silver Bullet Tuning has not responded to my requests from last week (if you know Les, let him know I am buying- either from him or another tuner)
Lavon at Firepunk has been recommended, but never replied to my emails over the last few weeks... (same as above)
Ryan at Hardway Performance is next on my recommended list

So what's your overall mpg avg at this point?

The third tank was the least impressive so far with only a .9 mpg improvement since adding the Fitch Fuel Catalyst. Granted, this was purely city driving, but I enjoyed the flavor from the previous tanks with over +1 mpg improvement.
1st Tank = +1.8 mpgs
2nd Tank = +1.2 mpgs
3rd Tank = +0.9 mpgs
The overall improvement [based on total mileage / total fuel] since installing the Fitch Fuel Catalyst is +1.1 mpgs.

Overall with all your mods what is your total mpg/gained mpg?

I'll continue to post updates after each fillup- below is the first
The truck just came out of Hammer Performance's shop. Upgrades include:
Goerend Triple Disc Torque Converter, 15SS model
Goerend Flex Plate
200* thermostat
Flex-a-lite dual electric fan
AFE cool blue hose- CAI to Turbo

These will skew the science experiment as many variables were introduced at the same time.

I'm excited to share my first tank came out to a cumulative 4.2 mpg gain. 20.94 mpg- my earlier math sucked when I thought I was getting 18/19 mpg.. I attribute 1.2ish to the Fitch Fuel Catalyst and the rest to the new additions. (probably driving with a soft baby's foot..)
The modifications you recommended to me on the DB forum 'lessons learned' have paid off.
Thank you!

I am seeing 10* cooler engine temperature. Now it hovers around 200*; beforehand it was 210* or the mid-teens.