Registration weight class on trucks in PA is based on the amount of weight between unladen and max GVW. Then they have a range for each class.
On a PA class C drivers license, you can single/combine, up to 26,001 (no air brakes). When towing a trailer, only a small part of the trailers weight (tongue 10% king pin 10% +) is on the truck.
My 5th wheel is 10,050 GVW and 7070 unladen registered at 10,050 uses a standard trailer tag @ $28. 00.
The cops and Penn Dot meant your truck can not gross over 11,000 lbs itself at anytime as weighed at its axles. Your 11,000 lb limit is not GCW, it's the trucks GVW only. So you can gross your truck to 11,000 lbs (including tongue/king pin weight) and be able to hitch to a 15,001 lb trailer (if truck is rated for it) and be legal as far as Penn Dot is concerned. That's if you have a class C drivers License good for up to 26,001 lbs single or combined. Your combine weights are only limited by your drivers license class and your trucks ratings.
My new 07 dodge is 6709 unladen and 9000 GVW, which is class three and I kept it that way when I registered it. Truck is rated 20,000 lbs GCW.
My 93 D250 is 5580 unladen and 8510 GVW and its a class 3. But I let the notary talk me into going with 7000 GVW to get cheaper tags as class 2. When I hitch to my 5th wheel, I'm over weight as far as my registration is concerned. If I'd had to do it over again, I'd of went class 3. But luckily I hardly tow with my old truck anymore. Truck is rated 16,000 lbs GCW.
Earl