might i suggest using those flow control connectors? the ones with the thumbscrews in the top? they control the exhaust air from the respective side.. the tighter you make the thumbscrew, the slower the piston pushes the air out of that side... thus if you want to make the piston go out slower, you tighten the side closest to the rod. if you want it to retract slower, you tighten the side farthest from the rod. that'll slow down that rush of air.. it helps to regulate the speed(if you get a big burst of air or a small one, it's still going to go the same speed pretty much.. good luck
p.s. those flow control valves are white with orange(im pretty sure) and BE CAREFUL screwing them into the piston.. the threads grind off really easy(they're kinda junky).. this morning i had to re-tap a piston because one of those killed the threads on the piston..
good luck