I don't really want to go that fast, but if I don't at least try to keep up with traffic, it seems that the truck just lugs if I get down to the 45-50 MPH range, not to mention, I hate being the guy going that slow. At about 3500, I can maintain 55.
I'm still feeling this truck out with the trailer. I don't usually tow at 80, just tried the "big hill" at that speed just to see how much I would drop at different RPM's. At those higher ones, something, I think the AC expansion valve, begins to sing, at least before the compressor cuts off... another reason to keep the RPM's down. I usually keep it around 70 on the 65-75MPH highways we have in AZ.
Regarding speed rating, Where do you guys get that? My ST came with 255/50 20's (It's an Adrenalin) that were H Rated (130MPH). I replaced the rims and tires with 18x9's and am now running 265/65 R 18 Michelin LTX MS2's T Rated (118 MPH).
I think you guys are remembering the Firestone thing, and that was the older platform (I have one of those too, a 2001 ST) and the truck itself was governed at 98. This one is 105. I don't think there is any car on the road with such a low speed rated tire. Even donuts are rated around 80, IIRC.