The simplest thing to do is to do a break even analysis. This ignores the time value of money, the reduction in the mortgage balance over the break even period, opportunity costs, and tax effects, but in today's environment with your numbers those things are probably minor considerations.
Your current balance is probably just under $131K assuming you haven't made extra payments against principle and haven't skipped payments due to hardship.
The difference in interest rates is 3.875% - 2.625% = 1.25%.
You'll save approximately $131,000 * 1.25% / 12 ~= $136.46 per month in interest.
$4,000 / $136.46 per month = 29 months to break even.
Since you plan on owning the property longer than that, it probably makes sense to do that refi. Of course, you should shop around and maybe get an even better deal.