Heavy 1/2 ton GVW option experts?

[Coley]

I've had a few of these trucks (almost all 1/2 ton) and I haven't been able to figure out rhyme or reason on how GM dictated the heavier GVW option (5400lbs vs. 5000lbs) on these trucks.
I've had 1/2 tons with the heavy rear spring option and overloads still showing a 5000lb GVW on the rating plate...and then my current truck with no heavy spring option listed on the build plate with a 5400lb GVW plate.
Has anyone ever figured this out fully? Then I've seen trucks with 6000lbs stamped on the lower front portion of the box by.....the dealer? owner? or? I'm not sure if this 'added' rating matches the plate rating in the door or not.
GM strikes me as not being the best on organizing their truck line as compared to the cars, engine numbers, etc.
Any info or insight on this?
All Good
Coley