First make sure the velocity adjuster isn't in too far. Some drive springs are stiff enough that you can actually mash the adjuster past the point where it increases velocity and actually starts to drop it again. The increased resistance can also cause a failure to recock.
If that's not the problem, FTR issues on STBB guns are almost always either a damaged/too stiff mainspring, a bad hammer o-ring, or a worn hammer/worn sear. In some cases can also be a sear spring that is too weak.