I have a problem I am unable to resolve when mining to DwarfPool.

• I know my Nvidia card can output ~13Mh/s
• Command "ethminer.exe -U -M" benchmark outputs ~13Mh/s berformance.
• I am able to start the Ethminer successfully including -U or --cuda to specify Nvidia card, but the miner does not go over ~7 Mh/s!
• I have tried the Stratum Proxy successfully, but the results are the same, nothing above ~7Mh/s!
• I have even tried without the proxy and directly against the Stratum  8008 port with the command: "ethminer.exe -U -S eth-us2.dwarfpool.com:8008 -O 0xWALLETID -SP 1", but still nothing over 7Mh/s!
• When I try the same miner against MiningPoolHub's eth pool with the command: "ethminer.exe -S us-east.ethash-hub.miningpoolhub.com:20585 -O username:x -SP 2 --cuda", then it mines around ~13Mh/s!

So what's the deal, where is the bottleneck?
Is it the DwardPool's server, because MiningPoolHub can reach these speeds with the same miner?
I have even tried previous version of ethminer.exe, I don't know what else to try.

Thanks!