Check that all 4 pairs of wires in the Ethernet cable are connected at both ends. CondoInternet had a number of cat5 buildings where they had only connected two pairs and simply recrimping the Ethernet connector got you gigabit.
Syncing at gigabit on Cat5 is common, even if a spec sheet says it's not l.
Syncing at gigabit on Cat5 is common, even if a spec sheet says it's not l.