Dave, on my pickup I just have 15 inch GM wheels (6 lug) that I picked up when I was moving away from the slightly more narrow 16 inch ones. I've never checked them...never had trouble but I usually drive at 60 and not faster than 65. On the GM Heritage pages years ago you could see an internal memo (appeared to have been written to dealership managers) stating the AD trucks had been engineered for a constant highway speed of 55 mph and were ok for intermittent speeds of up to 65 mph. I averaged those and figured with the improvement in tire design it would be okay.
