My suggestion would be to drive on gravel and apply the brakes. If only one wheel skids, then probably that one wheel has contaminated brake linings. If all the wheels skid, then there is something going on with the adjustment of the brake controller.
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch