Nice shot.
You're causing your drivetrain more stress by using 2Hi instead of 4. That's going to hit your torque converter a lot, and all that excess energy is going to heat. And the upsized tires don't help. Use 4Hi or 4Low.
I wouldn’t mess with the fluid. DOT4 is more hygroscopic - will take in moisture.
The smell of slipping is concerning though. Being careful and limiting shifts is smart, but if it persists, there could be binding in the release mechanism or additional wear happening from cold-related issues.
I found a fairly base OR for about $45K out the door, but had to have it shipped in from out of state. The manual is brilliant. Much better than the Bronco.