The gun club stuff gave me a huge heartache at the last pro am. Would not run in my benelli... I knew better, but bought 2 cases due to the price. I thought these spaghetti slingers would run anything with a good crimp!
By chance have you mounted a side saddle? If so and it is not the stick on kind, but the kind that mounts using the trigger assembly pins you may have slightly tightened the pins to tight to cause drag.
Always check loads with the gun loaded to as in magazine, side saddle, lights etc when trying ammo. You can use the loads for malfunction drills or sell/swap with someone whose gun they will run in / pump. Might make sure the bolt is lightly lubed as well.
One more thought have you put an over-sized cocking handle on it? Everything together might be just enough to wt it down. You can also get behind it a little to much as well and the action wont be able to work.
Is it a new gun? I ran a box of 3" and then some full power slugs through mine when i first got it and it runs fairly light loads loaded up. If you like the performance of the shells you can always order the lighter recoil spring.
Best with your frustration.