Rear Brakes pulsation

Have a six month old 2018 with 3,516 miles presently at the dealer this being the second time for the same problem within less than 500 miles apart; Rear brakes pulsating when slowing down from 40-30 mph the first time . The present time is doing it from 30-20 mph prior to a complete stop! First time they claim at the dealership rear drums where out of round, they turn them and problem was fixed for approximately 350 miles know they stated the last time the drums where turned the cutting blade in machine was worn according to the tech! They have been turned twice and shoes sanded as well , claim the shoes are not glazed or cracked. Told them that this cutting and sanding was shortening the life of the rear brakes and making then too thin to drive during rainy season next month. Refused to exchange rear drums and shoes claiming Factory would request those parts back to inspect and they have to attempt to correct it prior to replacing them in order to get paid! Claim they would replace them the next time! Will get truck back today and will see what happens in the next weeks. Would it lead to a Lemon Law Claim and or the factory Rep Involved in this issue? Don't know and don't feel comfortable with these problem thinking I will towing a 21' Light Coach in the Summer! Any Suggestions???