2010 Mack MRU

I have a Mack truck with a MP7 that has had problems with the SCR system for a while, I'm using tech tool to measure the flow coming out of the dosing valve but it doesn't meet the requirements. Someone before me changed out the DEF pump about 4 months ago, When I got the truck I found the DEF tank to be contaminated and the pickup filter was so plugged up it tore letting all the trash into the system. I changed all the DEF filters but I'm still not getting enough flow, so now I'm starting to think my dosing valve might be plugged, either that or the trash in the system ruined the pump. The pump is putting out the correct amount of pressure.