Well I got my new Glock 19 today, and I can't believe how stiff the spring on the slide is,

..also very strong mag spring to, I couldn't get all 15 rounds in the mag...to stiff.
Can someone tell me how I can tell if my Glock is a 3rd generation or 4th generation?
I love the way it points, I'm sure I will get a lot of years out of it, I can't wait to fire some rounds through it, but dread loading those stiff mag's..
crappie cowboy