Thanks guys,

CarlD: I only have a push/pull valve so it's either backwash or standard.

Spensar: Yes, I've backwashed several minutes past the point of when the water runs clear to be sure.

Waterbear: It's a push/pull valve. I took the 'plunger' out today and examined it. It's old but didn't appear to have anything wrong with it. I lubed the o-rings up again and set it back in. After vaccuuming and backwashing tonight I held just a little hope that the reseating the valve would make a difference but no luck. It's like a punch in the stomach to see the dirt spew back out after vaccuuming in 110 degrees (AZ)

Is there a telltale sign that I could look for if the valve isn't seated properly?

Thanks!!