I also have the same problem...
I have LED's in my flatbed, and my blinkers flash about a million times per minute. Problem is, our trucks use a flasher that has a circuit built into it to flash fast. I am guessing that some engineer thought this would be great so we'd know if a bulb was burnt out. Any how, Shelby Griggs also have this problem, and is working on a solution as we speak. He thought that a Tridon replacement didn't have the fast-flash circuit in it, but it does so he is trying to modify it. Other than that, nobody makes a replacement flasher for our trucks besides Dodge, and you already have one of those.
If I'm missing anything, hopefully Shelby will jump in here.