He is full of it! I have the DC and don`t have any issues like you were told. In 9 years of towing with it I have never wished I had any other type of hitch! Sounds like you need to step back and look at how you are trying to set it up.
If I had to guess I`de say....,1. you are light on tongue weight and 2. you are removing too much weight off the rear axle with the WD bars. both of those issues combined will give you the problems you are having.
I would do this, weigh the truck and trailer without the WD bars engaged. then weigh just the truck. with these 2 readings you will be able to figure out the full weight of the trailer and the actual tongue weight. then you can move stuff around in the trailer to arrive at the proper tongue weight (12.5%). and then set the WD bars for proper weight transfer. It took me almost a full year of towing to get everything dialed in perfectly! I have it set up so well I can do 10-12 hours a day (500-600 miles) with no problems.
