Tires

:'(We just traveled 4400 miles and didn't have a blowout, but only because we checked the new 15" Carlisle tires every 100-150 miles for heat and pressure. One developed a blister on the sidewall near the tread. After taking it off, we found a blister on the inside wall about the same size but about 180 degrees around from the other. I bought a Goodyear Marathon to see how it does. It is a 6 ply vs. the Carlisle's 5 ply. Both are Load Range D and I keep 65 pounds cold in them (which translates to about 72 pounds hot). Is there any reason I can't use a truck tire on the trailer? We did this years ago on utility trailers and small pop-up's. As soon as we went to a speed rated 12" or 13" radial car tires all problems ceased. (just be sure they can carry the load).
AND I weighed my 3124 and the axle weight was 4160 on one scale and 4240 on another. No wonder the old Load Range "C" Electra tires would not hold up. The D's are rated at over 2500 pounds of weight per tire. What has the factory recently switched to??