Brake Controller Problems??

I have a 2003 Duramax which has the RV 7 plug, but my boat has the 5 flat. I purchased the converter from the auto parts store but now it seems that whenever I use the converter, that my electronic brake controller will not work. Pretty sure its the converter or boat trailer because I tow 2 other trailers on a regular basis that have the 7 RV plug already and it works great with those ones? Dont know a lot about the controller, just know it doesn't work real well, and i'm taking a trip soon from here in Vegas towing the boat back to CO and want to make sure its working! Appreciate any input!!! The trailer is a dual axle boatmate holding a 04 Moomba XLV.