Can't PXE Boot some Optiplex 780s

We've got a bunch of Optiplex 780s that fail on ConfigMgr PXE boot with the error message:
    PXE-E53: No boot filename received

I have at least 1 780 that boots and images just fine so it's not a network issue. I can't find anything different between the good machine and the rest of them except the ones that are failing are newer.

BIOS A15
Intel Boot Agent GE v 1.3.81
Bad Machine Manufacture Date 7/12/2011
Good Machine Manufacture Date 7/21/2010

We're using MSFT ConfigMgr 2012 1610 v 1526

I see a lot of really old threads here re this issue that mention older BIOS updates solving it but we're running a much newer BIOS. Has anyone else run into this issue with the 780s recently?

Thanks,

-Steve