I can collect items from Pokestops but every time I go to catch a Pokemon they just escape and then run away. My level is 26, which may have something to do with it, but I just don't know.
If you are able to use Pokestops and battle in Gyms, you are not soft banned.
If you're noticing a lot of Pokemon running away, this could be due to your level being so high.
When you're high level, you tend to run into higher CP Pokemon. Higher CP Pokemon tend to run away more often.
See this answer for more info.
I read this information on Reddit but can't find the thread again: Apparently Niantic has implemented several sorts of softban now. If your Pokemon escape immediately every time right after they break free from the ball then you are softbanned as well even if you can still use the Pokestops. Normally it should work again after 24 hours...