Lots of info, here are a couple of my thoughts from your posts.
I also live in the country and use a truck as a truck.
Running mismatched tires in 4x4 is bad in a typical truck, because your transfer case doesn’t have a differential (unlike your axles), thus the difference in diameter forces one or more tires to constantly slip. This is hard on your transfer case. (I know you already got new tires since you posted that, just wanted to mention it for others reference.) You may want to find a used 235/85R16 to have as a spare tire.
As for the hard to spin tires, are you sure your calipers aren’t dragging slightly? You may want to get out and feel your wheels after a long drive for heat.
As for your engine oil having a red tint, are you running red coolant? It would seem more likely to me that coolant and oil are mixing than transmission fluid.
Instead of running no fan, you should consider getting a junkyard electric fan for cheap and wire it up to a switch in the cab. That way you can have a fan that you can switch on for when you have to idle the truck. I will admit I am a bit paranoid about cooling after spending multiple thousands of dollars addressing issues with my older trucks that looking back now would have been prevented by less than one hundred dollars worth of cooling parts that I ended up having to buy anyway.
The electric fan would also be useful for off-roading, if you drive for long periods in low range (too slow for much natural airflow) you could leave the fan on. A used fan would be cheap insurance against a motor overheating. I have an electric fan from a V6 Camry that I am going to swap into my Tacoma.
I will admit I am skeptical that forced induction by itself would increase the MPG of a gasoline truck engine. Forced induction usually accompanies other upgrades (headers, intake, custom ECM tuning, etcetera) that I would think would have more of an effect. Conceivably a truck that had been heavily modified (excess weight, excessively large tires, excessive wind drag) to the point where the V6 was struggling to keep up or being lugged could benefit from the extra horsepower, but I am not so sure about a stock-ish truck. Not saying it isn't true, but I am skeptical.
If you get paper receipts from your fill ups, just write the mileage on your receipts and you have an instant fuel log. Save your receipts until you have time to log or upload the MPG data, and then throw them away.
Oh and pictures are always appreciated.