Looking at your profile leads me to think you have a gage/sending unit problem. With a John Woods trans and a 6.0 cooler you should be fine. If the fluid is still pink/red I wouldn't worry, just keep an eye on it.
Tuners are great for hot rodding, sometimes not so good for towing. I also had a 99 7.3. Gage went to 300 once towing on flat land. I was more than halfway to my destination so I kept going. Never happened again but I did put a trans in it just to be on the safe side. The original had 200K on it at the time.
