I have a craftsman 16hp, 42 inch cut riding mower with automatic transmission. The mower quit pulling, belts are good and have tried to purge the transmission of air with no luck...

If no noise, check the hydro lock out lever at the rear of the tractor and make sure it is positioned properly, it might be stuck at the transmission, too. If it's noisy when you try to go forward or in reverse, check the brake assy (inside of right rear wheel) and see if it is sticking. Common for brakes to stick on these mowers.