I know that Grand Design switch from the Winegard clone (wasn't a Winegard but looks like one) to a King. I had a King on the old Puma and was not impressed with its performance over the Winegard. They were roughly the same.
When I switched out the Winegard clone on my Grand Design and put in a Winegard Sensar Pro. I am in a fringe area and notice little if any performance inprovement. I did not switch out the power converter as I could never get an answer if I needed to do that.
One thing I did find out is that the manufacturers are not cautious about tightening the antenna connections. The antenna connection on the old antenna was quite loose. It would be a good idea to check them all to make sure they are tight as well.