Yea they allow combo plates but clearly state on their signs 7500 gvw max. Iv seen heavier trucks on there too but I don't wish to be the guy with the 2500/3500 they day they decide to make an example of someone. Can you get away with it? yea probably but for how long is the question. On one of our old 1500s we used to own we had commercial plates on it for years and my partner drove it home every night. This was a short bed truck quad cab it was very small and was clearly under 7500 pounds. Still one night he gets pulled over and the cop says hes seen him doing this for years but never was in the right lane to pull him over. And all he did was drive one lousy exit each night. But eventually they will catch up with you.
Now as far as the 1500s go we always bagged a lot of lawns so they often were maxed on grass in the back. Then had a 2000 pound trailer with 2 mowers and all the 2 cycle equipment so around 5000 pounds give or take was the standard tow. Then you add in 2-3 yards of grass and it was enough to wear out the brakes at a very fast pace.
Actually the brakes did not wear out fast. For that load and weight that brake wear was normal. Most pick ups go around empty most of the time. Then when used the loads are only 200 lbs or less most of the time.