Most of the time, the problem with stalling on 5/3/1 is just that you should have started lighter, and I would suggest you re-set. And that COULD be the problem... but if everything else is improving than you probably did it right. Personally, I made a lot of gainst when I first started 5/3/1 bench - then all of a sudden I got stuck. I tried re-setting the weight, adding more light volume, doing speed/max effort work, and nothing worked. Then, finally, I realized it was a form issue.
One day I was just fooling around with different setup, ways of setting an arch and getting tight, and one of them just CLICKED. I have benched like that from that moment on, and although my bench still sucks it is at least improving, slowly but surely. I am willing to bet that form is your problem. You probably know that you are supposed to be tight, pull your shoulder blades together, use leg drive etc, but it probably just hasn't quite "clicked" yet. My advice is to 1) watch every single bench video you can.
So you think you can bench is an awesome start, but just watch random strong people on youtube. Check out the wide variety of setups and see which ones look like they might work for you. 2) post a video of yourself benching on here and hopefully some more knowledgeable guys will be able to tell you what to work on. 3) Go into the gym and just feel out your form.
The important cues are tight back (shoulder blades pulled together), squeeze the bar as TIGH as you can, and drivee your legs into the ground. You know when you see guys benching and their ass comes off the bench? You want to press your hips up like you are trying to lift your ass off the bench, but set your feet far enough back so that you physically cannot get your ass off the bench. Keep those points in mind, and just play around with your setup (grip width, foot placement, arch, etc) and try and figure out what works best for you.
Bench has always frustrated me, because I have always had to figure out form issues for myself. Other people "explaining" it to me never really helped. I know my advice is vague, but I think if you just study good benchers and feel it out, eventually you will figure out what has been wrong with your form, and figure out the best technique for you.