No offence, but let's assume that it flew ok before the alum shaft.

Make sure the fly bar is loose. When I installed mine, the flybar was way to tight. Remove the screw on the top of the shaft and spread the head slot slightly with a small screwdriver. Check the flybar. It should flop easily. When you tighten the screw, it pulls the slot too tight. Also interfers with the movement of the flybar. Look for any burrs on the alum too. Remove any found.

The screw is only there to keep the flybar on in a crash. I used a small piece of alum tube to replace it. The tube sits loosly in the hole and is secured with 2 small pieces of shrink tube on the ends. Doesn't have to be more than 1/2 inch long. It is a normal mod to use on any alum head.

Also check that the gear is correctley aligned with the motor.

If all this doesn't work, level the swash and start over.

Keep us informed.