Pull the 2nd chip of the two that work fine in 1 and 3 and then try replacing the chip with first one and then the other odd chips and see if all 4 will run dual channel as long as 1 and 3 are used without 2 and 4. Whew, confusing to type.
EDIT: To clarify I'm saying run only slots 1 and 3 but this will test all 4 chips for dual channel capability which I don't see you've done above.
EDIT: To clarify I'm saying run only slots 1 and 3 but this will test all 4 chips for dual channel capability which I don't see you've done above.