I have a one-speed pump that when the pump was cold and I started it up, it would struggle to get going. Once it was running it kind of surged all of the time instead of running smooth. If I shut it off and then right back on it worked fine.
Mine ended up being a bad startup capacitor on the motor. Maybe the capacitor is bad allowing enough juice to start in low speed but not enough for high speed.
Check this post and it will tell you how to check the capacitor. http://www.poolforum.com/pf2/showthr...t=hayward+pump