Ford is introducing a smaller Class 6 chassis cab truck next year called the F600. It will share many of the components of the larger F650 but be the same dimension as the F550. This 22K lb GVWR vehic...
One small detail - that GWVR at least in CA requires replacing engine every few years for smog reasons. I remember that like 20 years, so not a big concern for guys who replace truck every few years, but that will kill resale value on older truck.