51 is near the top of the acceptable range, VM will tell you there are many connections with higher levels (~54) that are working just fine.
All your other data looks good - what issues are you actually having?
Have you got a BQM running and what do the Network logs look like?
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John
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I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router +2 Airport Express's. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.