I don't think a +4 run differential is a problem. It probably only takes an 85 win team to make a WC and a +4 RD puts one on that pace.
But further to that, the RD is trending the right way. A lot of this is guys busting out of their slumps and a lot of it is just finding the right 26 guys for the roster.
Wagner, Roden, Barnes, and Lovelady were replaced by Barger, Varsho (for a while anyway), Fisher, Fluharty, etc.
Also, I think we've got good depth on the player position side as well as in the bullpen. As other teams deal with injuries throughout the season they will stumble but the Jays should remain pretty strong so long as we don't get any more injuries to the rotation.