Attention: TDR Forum Junkies 
our twin 3500, 2001. 5's have had the exhaust man bolt problem. one of our trucks was sent into the dealer to have the collars put on the back and front bolts, as per the tsb. when the ext manifold was ready to be re-installed, they found that the holes did'nt line up with the head, and had to order a new manifold. after replacing the entire manifold we found a 4 inch crack on the bottom of the old one. when i got back to the shop and looked under the other truck's hood, after being fitted with the retainers, and guess what? yep identical crack, identical place. now logic tells me that the problem is egt's but both trucks have gauges, and both drivers tell me that they have never gotten them into the red without backing off, i beleive them because when i've ridden with them i watch how they handle the hard pulls and seen them keep the egts at a reasonable level. {and that includes me, when i drive one} 6 speeds with 275's alone shouldnt create enough heat for this should they? just think of those without the gauges, anyone had this problem? 
