Let us know what you find out as I hope to go down the same road in the near future. Waiting for information on the 2015 Sierra 3500's. In the research I have done, the frame and drive train remained the same as 2014, the body and bumper changed and they beefed up the class V hitch if yours came with the 2 1/2" receiver but I would bet that Torklift would still work. Happyjac probably has some issues as the bed is all new and as you already found, the new corner plastic bumper steps are not going to like Happyjacs bumper bolts.
Keep us updated!