Low Pressure Delta Shower

I just installed the trim and shower heads on my new remodeled double shower. My plumber installed the rough in delta r10000 valve and the delta r11000 diverter. I just installed both shower heads and both the trim kits for the valves. When I go to turn on the water, it comes out at a decent rate, and then slows down. When I turn the diverter to the other shower head, it does the same thing and when i turn it again so that both heads are on, its almost nothing coming out. Both shower heads are 2.0GPM and I also turned the temperature as hot as it can go. Any help?

have you removed each head and flushed one at a time
you may want to contact delta ..... I think I read about this
on another forum(plumbingzone)?????this came up I think there
was a peice of plastic in there???one guy said he wacked the top
of the valve body (6) times and it worked calling delta
would be my first step after flushing with no results