"As I have had rigs with gcwr's LESS THAN the gvwr of the truck."
You are saying that the truck by itself had a higher rating than it did including a trailer?  (Gross Combined Weight Rating). Seems unlikely to me.  What year and model were those?  I know these acronyms get confusing.
"The  Gross Combination Weight Rating (GCWR) is the sum of all GVWRs for each unit in a combination-unit motor vehicle. Thus, for single-unit trucks there is no difference between the GVWR and the GCWR."
By that definition, GCWR can never be less than the GVWR.