Did you fill the flagpole with spray foam or just at the joints?

 

Poles are normally the perfect diameter to insert 1/1/4" pvc tubing down center. next use stainless steel self tapping screws long enough to connect the slip joint of the pole sections to each other AND go into the PVC piping- in the center of the aluminum flag pole- did this to my 20' pole and it has no problem in the wind-- sunk it into grown about 17" in the sleeve provided with pole kit.