Hello Ed;

I’ve used pull-pull for the elevators on a 1/3 scale Pitts with great success. You want the path of the cable as straight as possible. The more direct, the less slack that you will have to deal with in the long run. May I suggest taking the cables back out and stretch them with weight for a week to ten days. Those will now probably be too short to reuse. With new cable, prior to measuring and cutting, I hang a 5-10# weight in the center tying the ends to rafters or something high. This takes 90% of the stretch out of the cable. As said earlier post, take the plastic tubes out. The wire will cut it. Believe it or not, your cable still isn’t tight enough. I would up grade your clevises to more heavy duty. The secret to getting the cables tight, is to get them as tight as you can with everything crimped. Leave plenty of adjustment with the clevis bolt. When you think it is tight, take the control horn off the servo and further screw the clevis more tight. Do not twist the cables. Tighten them up until you have a hard time putting the control arm back on the servo gear. It is pulling equally, so it isn’t hurting the gears.
You are worried about flutter with pull-pull. There is actually less chance of flutter, due to the control surface is always being pulled in the opposite directions. A regular set up with just a push rod, there isn’t anything to balance it out other than the servo’s torque.