Hello, this topic is relatively old but, I want to share what we did in a similar 7500 to 7800 migration with FOS level 7.1
Our gigE ports were stalled at "no_sync" after we connected the cables. After searched it from many ways, I saw a portcfg parameter which is "autoneg". So I don't know why but this setting came as enabled.
After disabled it, port became online...
No syntax found on the admin guide but it is like:
# portcfg autoneg ge0 --disable
Good to try..