I put 285/75-16s on my truck and have had no problems. I do have the Powerpup to adjust the speedo. It might take your tranny a little time to learn the shifts for the 285s, but I have had no problems. I didn't notice any loss of power either. Of course, I hardly drive my truck at the stock setting, (TST advances the timing set a 0,0) but even when I do, I don't notice any difference driving it except it rides better than with the pizza cutters on it.
Yes, but they were crap on my truck. The other truck I had 245s on I ended up rolling....now I don't blame the tires, but I like to be more sure footed than the little contact patch affords me. I believe that our trucks should have come with 265s on them anyway. Although, I think GM is in cahoots with the tire companies....give us crap tires and tell us that if we change them you will have to put the 245s back on before troubleshooting any "driveablilty" problems. I don't see what the problem is with the allison when the hummer comes with 35" tires on it off the line. Also, with those pizza cutters on it felt like I was driving on stone wheels because the ride was so harsh. I did lower the tire pressures, but it didn't seem to help. I'm not worried though....I am happy that my truck looks like a truck instead of an oversized passenger car.