Trouble codes P0440 and P0410?

2001 Chevy blazer 4.3 automatic. i have trouble codes p0440 (evap malfunction) tied in with p0410 (2ndary air malfunction). I replaced the air pump and new hose assembly. Light came back on with same two codes. (The pump sucks in air and works fine). I think I may have found the problem. I traced it to the 2 air check valves that lead into the manifold. If these are stuck open and/or detiorating, the evap system isn't achieving enough vacuum during it's test so the pressure drops and sets the p0440. Does this make sense to anybody or am i off base?