good to fair for SNR and AGC seems okay to me. The error counts do seem high, but they are correctable. A drop amp will probably help with SNR and AGC if it's a high quality one. It probably won't help with the error counts. It could be that the errors are originating somewhere outside of the cable delivery system, i.e. upstream of where the HD signal is inserted into the cable system.
Out here, when we have break-ups on cable, there are also break-ups on OTA. It might be worth a service call and have them evaluate your signal.