the servo I have used in my 2 H-9 planes has been the, futaba High Torque low profile retract servo, it has 92 in oz of torque at 4.5V I tried to look up the HT 755 and couldnt find it but there was a HT 75 retract servo listed and it was rated the same.
the recomended servo from Horizonhobbies is there JR High torque at, 260 oz in which seems like over kill since my futaba's work great.
if your retract servo is not lifting the retracts then it might be binding which can lead to a serious drain on the battery .
another thing I did was to make sure the push rods were 180o from each other and were cut short enough to clear when rotating H-9 has a diferent photo in there instructions.
the pushrods were offset from each other just slightly which didn't give the ammount of travel needed.
I found when I was setting up the gear that it was unworkable and was binding, after I clipped the ends of the pushrods,just enough to clear each other, there has been few problems.
the gear take some messing with it took a couple of days of fiddling with it to get them working to my satisfaction.