Well, I did a little digging on the PA DMV website today.
Here is the quote for licensing....
CLASS A (minimum age 18): Required to operate any combination of vehicles with a gross weight rating of 26,001 pounds or more, where the vehicle(s) being towed is/are in excess of 10,000 pounds. Example: Recreational Vehicle, when the towing vehicle is rated at 11,000 pounds and the vehicle towed is rated at 15,500 pounds (total combination weight of 26,500 pounds).
This means that you have to have the Class A Non commercial license if your truck and trailer is over 26,000 lbs, and the trailer has a GVW of over 10,000 lbs.
In my personal case, my truck GVW is 11,000 lbs and my trailer is 14,000, so I am OK with my standard Class C license.
I looked up registration, which is what this thread was originally about, and it states for vehicle only. You are registering the tow vehicle for GVW not GCVW. (unless hauling commercial)