Are you directing enough return water through it? I find that with my Polaris 360 and a single 2-HP pump, I have to direct almost all of the return water through it, to get it to go fast enough to make it up the slope from deep to shallow end, and then work its way around the pool and keep moving - even when it hits the steps for a bit.
I have issues with it hitting the steps and sitting idle for a while, till the backup valve kicks in, but the wheels keep moving throughout this time.
You might also want to check to see if you have a leak along the hose or even in the cleaner itself.