Are you certain that the keg was at 34F? If it was warmer then that then your carbonation volumes would be lower.
Priming sugar is not necessary if you are force carbonating. You just need to make certain of the appropriate pressure for the actual temperature the keg is stored at.
Was the beer carbonated to your taste i.e. fizzy enough or was it rather flat? If there was enough carbonation but not sufficient head and it could be the beer itself that is causing the problem. It may just not have enough proteins and dextrins to develop a good head. Or it could be the inner diameter of the tubing vs. the length...
More info here, I guess is what I am saying.