I think the weight of the HT will make the slider a little difficult to deploy. We have a similar set-up and I find that the slider is difficult to move. I would suggest you spray some type of lubricant on the slide rails and see if this helps. On mine, sometimes I have moved the slide lever to the slide will go back, pulled forward slowly and applied the trailer brakes and this will move the hitch back for you. Just do go too fast. We don't have the pro slider, but have used this one since 2003 in three different trucks. Just be sure to make sure you are securely hitched if you try the pull-forward and put on the brakes method.
2012 GMC 2500HD D/A Crewcab
2012 Jayco Eagle SuperLite HT 26.5 RLS
2009 Crestliner Superhawk 1900
2013 Polaris Sportsman 550 EXP
2008 Polaris Sportsman 700 X2