Yeah, by the 2006 model year all the older chassis with single filters had been sold under 2003-2005 models.
Consider not changing the secondary, engine-mounted filter each time the rig is due for a filter change. The primary filter & water separator catches all the big crud that typically comes out of the underground storage tanks, and the secondary is there for the fine grit that escapes. It's a gamble, of course, betting that not much fine stuff got thru to collect in the secondary. Still, the risk is just on-road performance loss and limping to a place where the filter can be changed. It still protected the fuel injector pump.