How are they stalling? Are you missing the first set or getting the first set but then missing sets 2 and 3?
Ex: 4,4,3 or 5,4,4???
Check your rest times between sets. If you are generally getting the first set but missing the last 2 then use the 1x5 + 2x5 backoff method. If you are missing the first set then try switching to 3x3