The D-series isn't really supposed to be a copy of any IRL pickup- While it does draw elements from certain '80s and '90s American trucks, the D-Series is mostly the devs own design.
the body shell is 90% GMT400, the original front end is a bad knockoff of a GMT400, the pre facelift is off a bullnose f150, the post facelift is sort of a mix of an early 2000s f150 and superduty, and a GMT800 (both pre- and post-facelift). the engines are pretty much direct clones of ford modular engines, having an OHC layout, the 6.0's turbo is even set up like a 6.0 powerstroke. tl;dr it's a mix of the ford and the chevy.