I have a 2013 standard bed (6'6") Duramax and my camper is about 6,000 lbs loaded. 750 lbs tongue weight. That's what my numbers are without a topper.
The manual will tell you that using an WD hitch with that kind of weight is optional (up to some ridiculous number...I forget what it is). I use an Equalizer hitch anyway.
You have to be careful and patient when setting up that light of a camper using the EQ. The 2500HD won't respond to your adjustments as quickly as the 1/2 did because of the stiffer suspension and it's easy to add too much WD which will make for a rough ride (ask me how I know). Once the hitch head is set with the correct number of washers (I use 4) moving the L brackets up will add more WD.
On my truck with the WDH engaged at the 5th notch from the bottom on the L bracket my front fender is 1/8" higher than unloaded. At the 6th hole it's 3/8" below unloaded. Don't ask me why there's that much difference but the ride is a lot stiffer.
2013 Chevy Sliverado 2500 HD LS Crew Cab
Duramax/Allison, HD Tow Package, GCWR 24,500
2017 KZ Sportsmen S330 IK