I'm having a hard time manually locking the slide of my new P226, I usually grab the front slide w/my left hand and engaging the slide stop release w/my right thumb while gripping the pistol. Racking the slide is quite stiff, though it had already 300 rds fired on it. I never had issues w/my P229 9mm DAK before and with my current X5. Any inputs?

P226 recoil spring and stock mainspring are pretty stout.  My wife has a hard time racking my P226s (not implying anything here).  It should loosen up a bit with time.

One thing that helps me is locking the hammer down before I lock the slide––this way you're only fighting the recoil spring.  Of course, ALWAYS keep your finger off the trigger.

Front cocking serrations (SCT/BW) help too!  Otherwise I grip at the rear.