Ford 7.3L Power Stroke (1999-2003) :: F350 DRW 4x4 Transmission Temp High

I will start off with saying I am posting this for my dad. His truck is a 1999 F350 crew cab DRW 4x4 auto 7.3 with about 189K miles on it. He is leaving wednesday on a cross country road trip pulling a 40FT 5th wheel (no idea the weight but the thing is huge). He has glowshift gauges installed, one of which is the trans temp gauge. I believe the transmissions on these are 4R100, but I am not positive about that, but I'm sure many people here will know. He just told me that he had the mechanic he goes to replace the pan gasket on the transmission because it leaked quite a bit, just as a precaution. He also had them replace the brake booster as it was leaking inside by the brake pedal. When he got it back, he said he was driving it, and the temperature started going up to I believe 220 degrees not pulling anything. He said since he installed the gauges it has been between 180-190, and it jumped to 220.

What this could be. I have read that the TFT sensor can cause this issue, but it would throw a code and possibly go into limp mode. He has no check engine light and it was driving just fine. So the temperature is just all of a sudden high. Fluid level is fine, was checked after about an hour of driving, is red, and doesn't smell bad. I am suspecting the temperature isn't actually hotter, so there is another issue. It's only a big deal now because in a few days he will be dragging a huge 5th wheel behind him.

Last year, we towed some pile of crap 5th wheel down to our city for somebody with his truck, and we had to pull over halfway back because it started to smell like something burning. We think it was the trailer, as the brakes were questionable on them. When we got it to the people we were delivering it to, when we left, it wouldn't shift passed 2nd gear. He only lived a few miles from there, so he drove it home, parked it, then went out the next day and it was fine. He had the fluid flushed later and that issue hasn't come back since. No other work was performed on it since the pan gasket a few days ago. I am not sure if they are related being a year apart, but figured I'd mention it anyways.