My 12 Ram 2500 CTD won't lock the 5er brakes. I replaced the OEM TBC with a Tekonsha and it would lock up the brakes. The Ram wouldn't lock up the brakes on our previous TT either. Gave the Tekonsha to one of my sons and went back to the OEM TBC.
The strange thing is I've been in sudden stop modes while going 45-60 mph and had to hit the brakes hard on the truck with the OEM TBC and the truck and trailer stopped great. Just guessing here but I wonder if the newer TBC's have a different algorithm than after market TBC's. They won't allow a slow speed skid but will allow the power necessary at higher speeds to stop the trailer.