Do you have any damage exhaust pipe, like a crunch pipe? I'd take the tuner off and see what you have then. My truck runs hotter with the larger tires, about 800 deg. and with the 5ther in tow at 70 mph around 1100 deg to 1200 deg.....
Dogman,
That was my first though, so under the truck i went ! Not a friggen dent of crushed spot anywere! I am running 305 70 16s ,dont know if thats helping any. I did run it in the stock setting and I can still hit 1100 deg.
Well on the other hand, I'm thinking gauge or probe are bad or a grounding problem with gauge and/or the probe is to deep in the tube. The probe is only to be about haft way in the tube or the tip in the center of the tube. On the grounding thought I had a gauge that was not giving a good reading and would bounce. Found out that the gauge need/had to be ground to the motor and not the body or batt. for ground. It had something to do with the probe. To this day I still dont know why it need to be this way a ground is a ground. But hey it works right now.
The probe grounds to the engine and the gauge should be also. Actually they all should be tied together at a GROUNDING POINT, like the batteries or the starter.