I've pulled our 5 ton camper a fair amount with my '65 F250 first with a stock 390 and now with a 482. In between those two FE's I acquired a 2002 Duramax. Here's what I've seen. (BTW, gross weight with the F250 is 7.5 ton, with the Duramax its 8.5 tons).
Stock 390: Power was barely adequate. Many interstate hills had trouble maintaining 55mph even with a run.
2002 Duramax: All the power I want/need. Some hills it barely holds speeds in overdrive. More challenging hills make it drop from overdrive (5th) down to 4th. Even then it has no problems holding 65mph. I guess I could hit 70 but that would be redlining it and the power curve drops straight to zero at 3200 rpms. Point is, that's all she's got and that's enough to maintain reasonable speed anywhere.
'65 F250 with 482: On the same hills where the Duramax hits a wall will actually accelerate and leave the Duramax behind. I can only imagine this 482 will run with any of the factory tune pickup truck diesels until around 2011 when the Scorpion platform came out ..those engines have obscene pulling power for their class.
MPG pulling 5 ton
-Stock 390 was 7-8
-Duramax is 10-11 on regular diesel. 8-9 on the danged biodiesel
-482 is 6-7 but I believe I can beat 7 if I install an overdrive since it has the power to pull at a relatively low rpm for a gasser
FE can make a good puller. Just need to consider all the costs, available parts, end use, etc. I honestly don't know enough to say an FE would be good in a C600. All I can say is that in my case the right FE will out pull factory tuned diesels before 2011...certainly a factory 7.3 IDI. Maybe the pre 2011 diesels would win out in higher elevations like in the rockies...I don't know because I haven't pulled an FE there. East of the Mississippi I believe the right FE will hold its own in terms of pulling power.
One benefit to the FE is simplicity...particularly with its fuel system compared to any modern diesel. Something to think about with a classic truck where repairs away from home may fall onto the owner.
