I had that same problem on 6 volts. I sent them back and just got the replacements last week and they seem fine. I went and bought 6 more and tested them and all of those seemed fine.

If they work then for the price and 150 ounces on 6 volts you really cannot go wrong. I've replaced all my servos on the ailerons on my GP Ultimate (4 of them) then all but the rudder on my Showtime.

All are on Li-ION regulated to 6 volts