For anyone still having this issue, I just installed the Westin drop steps on my 19 GMC duramax. Like everyone else it seemed the DEF tank was in the way, however after removing the tank cover and taking a grinder to the back side of the supplied bracket that is supposed to go in that location you can get that bracket in between the rocker panel and the DEF tank. You also have to take a grinder or a file and take some material off the bracket where the rocker panel half rounded tab goes so the bracket can slide around it. The stock hardware won't work however. I just dropped a bolt from the top and threw a washer, lock washer and a nut on the bottom and tightened it up. I don't think it's possible to connect the top part of the bracket unless you drop the tank down. At least my hands are too big to fit between, I'm going to see if my son can get the bolt started as I think I can get an offset wrench on it to tighten. Anyway, you can get the bracket they supplied in there without removing the tank, just takes a bit of modification to the bracket. It feels sturdy with all the other parts bolted up. Oh, you also have to cut out a section of the DEF tank cover so it can slide past the bracket that is now obstructing the tank cover. I don't think that's a big deal though.
