There's a guy back home named Sanders, he has a built Mack he calls the Silver Bullet. It will pull one hell of a sled...
I used to work as a grease monkey/go to guy for a small trucking co, mostly KWs with Cummins motors and rockwell trannys. There was one Pete, it had a 425 Cat and an Eaton Fuller tranny. Boy the driver tore the clutch out of it once, it made life a living hel for about two days. Also had one old KW with a sleeper. Had a juiced up Cummins, but it ate rings all the time. What a pain in the arse, a gallon of oil every couple of days. But man would that truck pull...
On the other hand I occasionaly have the (dis)pleasure of having to drive the five tons and seven and a half tons, made by AM General. If you ever have the opportunity to drive one of these rigs, pass on that.