Most Likely Local Rank Factor Holding Me Back?

Have a site and for all our primary keywords coupled with the city name we are in we are #1 on the organic results. We are performing the test searched from a client workstation 3 miles from the business address. So say we are in Seattle, the Google Places for business is within blocks of what Google considers to be the center point for Seattle, WA and we are searching from a employee's home about 3 miles away in Seattle.

Up to this point we were not only #1 organic, but number #1 also in the local 3-pack for all our primary keywords. We have 2 5-star reviews and the other 2 competitors in the 3 pack have 0 reviews or sometimes 1 review.

We are obviously trying to figure out the most likely local ranking factor(s) that are all of the sudden preventing us from making it into the 3-pack like we were before. We've made no on-page changes. The only thing I can think of is that we were once a week doing the Business Places Posts (a feature Google introduced a few months back) and doing more social media (Facebook, Twitter, etc) posts than before. The other thought is we haven't gotten a review in a long time - but as I said so of these other in the 3-pack have NO reviews AND rank lower organically, AND are not physically closer to the client's search location. So my guess is that's the difference but it doesn't seem like those should be very significant LOCAL ranking factors except for the Business Places Posts which it looks like the other competitors are NOT doing anyway!

Any guesses?

I would say honestly, you need to update more to keep your content fresh. Doesn't mean you have to change on the page text for every single page, but go through the most popular pages and make them better. This will show Google you are spending extra time making these pages better as well as also showing that your results are current. If your competitors are updating potentially and you aren't, then you are at a disadvantage.