These motors have an initial efficiency learn function that needs to be modified with a programming tool mars motors sells for it in order to match the motor resistance to the equipment it's installed in.
I learned that the hard way after buying this unit used and ignorant of the fact, installed it, had it behave crazy, then troll the internet to find a video about installing these produced by a distributor and published on you tube.
$70-ish dollars for the tool and considerable pain of learning curve later, I got things right, and made the very low price paid well worth the "lost free lunch", I thought it'd be a courtesy to the next guy in line to put my caveat out there, but as Ben Franklin was quoted something like "your money is all in your brain" - fear not and tool on.