Well not the Shield but an MP9CSorry if I missed it earlier, but how old is your gun? I found mine to be pretty stiff when new, including rotating the takedown lever down. Once I got it field stripped the first time, and got a little bit of lubrication on that lever and end of the recoil spring assembly, it became smoother, and continues to get easier every time.
If your slide doesn't lock open with a magazine, and you can't "thumb" the slide lock lever up and hold it open with no magazine, it sounds like something's not aligned right inside your gun.
I had to use a dowel to get the take down lever to move when I first got the gun
After about 200 rds It could be done with my thumb
Same for the slide stop/Release