I searched the forums for stalling on 5/3/1 and I recommend you do the same. Too many different answers to repeat here.
The initial answer is that if you miss the prescribed reps for a couple weeks on one lift then change your TM based on your most recent rep max. This is bare minimum reps not plus reps. If you get 1 on your last set of 5/3/1 week then keep going like normal.
Another approach is to plan a set number of cycles and set a goal and work backwards. Example: Deadlift 500 in 20 weeks with current 475 Deadlift max. Set your TM at or close to 500 for the 5th cycle (which would be week 20). Set TM at 490 for 4th cycle, 480 for 3rd, 470 for 2nd, and 470 for 1st.
This is just an example based on my understanding of Jim's comments in another thread addressing this exact topic. I could be a bit off. I haven't tried this on myself yet. Just trying to help.