99 f250 starts and eventually runs till it bogs and dies

[bojack16]

I have the #3 and #8 failing the contribution test, just replaced those 2 in Feb of 11. Took them back out as they were under warranty and sent them back, they say they tested fine. Before I found those I had p4076 epcv code come up. Put the injectors back in cleared all codes drove it, run fine for 45 mins or so on back roads, hit the interstate and it fell on its face and almost died. kept it running run diagnostics and the 3 and 8 come back as a fault on contribution test. And the ecpv come back. I am stumped the truck runs fine then goes to hell, why would it run good and then fall on its face if the injectors are good and why would they fail the contribution test. Any help would be appreciated thanks