So after selling both my r model dump and roll off a few years ago, I very quickly started missing them and looking for another. My perfect truck would be heavy spec short wheelbase dump. A Tandem with 58 rears 18 or 20 front, 350 or more hp and a good trans. Well, I just purchased a 86 RD600 in decent shape and well kept. heavy spec, but a little less hp then I wanted having the em-300. I actually don't mind the 300 hp with the torque it puts out and knowing its durabilty, but my real complaint is the 7 speed T2070 trans. Great low end power and great highway speeds, but really wish i had more gears to split to get it to speed. I feel like i am making the motor work to hard with heavy loads (70,000 lb). Was really hoping to swap out for maybe a mack 12, 13, or 18 speed. Any suggestions?