Thats Sounds like a heck of a note. I used to be at a vol. fire dept with my uncle and they had a 534 also and i don't recall it ever getting hot. it had the original carb though. well of course he worked on the trucks so they were in pretty good condition. sounds odd to me. how high is it reving? How often is it to the floor (ie. all the time, 50% 75%)? try letting up a bit on the throtle, nothing to slow you down but enough so were it won't rev out as high. not an expert but try it when you aren't on a call. take it out if possible and expiriment with it. find it's sweet spot.

1978 F-250 Ranger Explorer 4x4
351M, C6, Np205, D44 Front, D60 Rear 4.10LS