I personally think that tapering off is an individual problem. Some people take months to go from say 10 mgs. down to 9, while others start at a much higher dose and can taper off faster until they get to a lower dose. Your body lets you know when to hold steady. I started at 10 mgs. and am now down to 2 mgs, but it has taken 16 months with fluctuations along the way. My body is telling me to stay at two for the time being with just the occasional stiffness when getting up from a chair. After my rheumatologist started me on Plaquenil (200mgs twice a day) I was able to taper off every two weeks from 8mgs down to 2 mgs today. So far so good.

7 mgs. is tough because you're low enough that your adrenals need to kick in but they were sleeping while the prednisone did their job. Hardly a medical explanation, but getting below 7 is a challenge for many. And sometimes it's necessary to stick it out because it's not that the PMR is worse, it's that the adrenals aren't doing their job. And you need to give them time to wake up. Once you stabilize, you could try heading down again very slowly. Half mg. at a time.
Trouble tapering for me involved the return of some symptoms only not as severe as when I was first diagnosed.