I'd almost certainly say give this chassis a try first and see how it does (similar to what I'll tell someone with a stock dually getting a big TC.) Having said that I always really liked the idea of the GMC T series cabovers as a platform with the admitted drawback of no 4WD, but if you don't mind that it seems like would be your ticket. 3K pounds is gonna get used up quickly :). I knew that around the time of the bailout they stopped production of the TopKick and Kodiak but was never sure if they also killed the T series? I think the last model year of the Kodiak/TopKick was 08 or 09 so they had already gone to post emissions......we looked at buying a new 08(?) with the emissions. it was economics and possibly poor management choices that killed the line. Anyway, maybe they stopped bringing in the large Isuzus at the same time and for related reasons
