Please bear with me here...I assure you i am not trying to insult your intelligence...just running through the things I have seen with thousands...literally...of semi-auto handguns.
The action you describe where the slide is going forward slowly like it is gummy inside is absolutely NOT normal for the Beretta...it has one of the smoothest slide actions of any unmodified pistol out there. This is definitely suspect. What type of lube are you using? What are you cleaning with?
Try taking the gun down and cleaning all traces of lube off of the slide and frame rails with a degreaser, then use fresh CLP which has been shaken well before use to correctly distribute the lube into the suspension. Empty, with no mag, the slide should move very freely back and forth now. If it seems sticky only when feeding a round, clean the barrel...specifically the chamber area...really good. If you have shot lead bullets, use a wire brush with a small amount of #000 steel wool wrapped around it to be certain ALL residue is gone. (Eventually, failure to clean the chamber well can set up a condition of false head space, where the case stops before it is fully inserted on the feed stroke, sometimes not allowing the action to lock...this is not what you describe and/or show as happening, however)
You might also try cleaning behind the extractor as well as possible with solvent, a brush and canned air. If the extractor is not moving freeley it can cause issues when the case is trying to rotate up and into the hook/claw. Ditto for the breech face area.
Definitely try a new or near new factory mag. If it still seems sticky with this mag when hand cycling, you have a parts issue somewhere...perhaps the mag catch is slightly too high, allowing the top of the mag to contact the slide, or something else. Should this be the case, run...don't walk...and send it to the factory.
My guess is that your mag springs are weak and that new ones will solve your immediate problem, however. Use the +10% Wolff springs and spend the $10 or so for a new recoil spring too as both BobCole and Dog1 suggested...can't hurt.
As a last resort send it to me...I can use another 92!
Good luck.