The 26k combined law goes by GVWR of both the truck and trailer, not actual weight. The GVWR of both must not exceed 26k, although, you have a 2500 with a GVWR under 10k so you are exempt in most states that only impose that law on trucks that have a higher GVWR that 10k like 3500's do.
So in Texas, if a 3500 only weighed 8k, but had a 12k GVWR and the trailer it was towing only weighed 15k, but had a GVWR of 20k, then that would put you over the 26k GVWR limit requiring a CDL even though the actual combined weight is only 23k.
However, as I said, vehicles that are 10k GVWR and lower are exempt from this in most states because these laws and weight limits were written so long ago(like our truck class limits) that they were never added because nobody would have thought that a truck below 10k can actually tow that much back then. Back then, a DRW 3500 had a GVWR below 10k or just a hair above it.