Polaris running toooo slow..

My Polaris 480 w/ booster is running too slow. I checked the water pressure coming out of the wall and it seem normal (i.e high volume w/ booster pump). The back up valve seems to be working normally, where water shoots out when backing and nothing come out whe running foreward. There are no leaks in the hose. I replaced all the belts last at the beginning of the season and the wheels all turn. But it is really crawling slowly and , there doesn't seem to be a tremendous amount of pressure coming up through the venturis. Although I'm not sure aboput that as I never paid too close attention before. There is enough pressure coming up through to have tha bag standing straight up and it is picking up debris, but it is definetely moving cery slowly.

Any Insight?

Thanks in Advance

Correction. It's a 380. Update. I spoke with Polaris and they are stumped as well. They are going to send me some parts and something to test the water pressure. But it seems fine to me. Everything is working properly except that it moves about half as fast as it should. I tool apart and the belts are fine, proper tension etc. Water shoots out of all the proper orifices with good velocity. I am stumped.
Please help!

Well I hope you are not having the problem I was having with mine. Exact same symptoms, but here was one other - I was loosing water from the pool. Turns out there was a break it the pressure line under the ground. Everything seemed fine except for water loss and slightly slower polaris movement dues to less water flowing to the polaris.

Be sure the backup valve isn't leaking "on". I had to replace mine as it was stealing water pressure. Found one on ebay....

Thanks for the insights. My pool level is fine and my back up valve doesn't leak.
Could the pressure relief valve cause a drop in water pressure? It does not pass any water, but mine seems a bit bugggered up. I'm reachin here, but am at a loss. Polaris is sending me a fitting to check the water pressure. I guess I will have to wait. One othere thing I am going to check, is to see if there is anything obstructing the flow behind the wall fitting. With the washer adapter in there make for a small hole, maybe there is something clogging it. Like I said the pressure seems fine, as I run out of the water, the water shoots out of the adjustment nosle about 20 feet and out the venturis about 10 feet.

Thanks for the suggestions so far. any more would be appreciated.