I appreciate the feedback from all who responded. I think my training plan is clear. More miles. My typical run is 5 miles but I also typically take a day off between runs. To hit the weekly mileage you guys are suggesting results in me running almost every day (at least six days a week). I see now why “easy” needs to be “really easy” as six/seven days a week at 5 miles (or longer) a run will likely be somewhat of a shock to my legs (although probably no worse than the interval training I was hammering on the treadmill). I like the feeling of running fast (or I should say running hard since I am not very fast) so I will affirmatively rein in that impulse to hit the weekly mileage goals.
By the way, on an unrelated (although still running) topic, I have a question about shoes. I don't know much about running shoes or my foot…I have no idea if I pronate, overpronate, have a high/low arch, no idea at all. When I started running last year I did a little research, read a bit about barefoot training/minimal shoes and how training in minimal footwear can provide better running mechanics (ie midfoot strike vs heel strike etc). Since I was a nonrunner I took the view that I might as well start off wearing minimal support footwear and I have been training in Nike Frees for the past year. These are the only running shoes I own and I run on the treadmill, road, trail etc. in these shoes. I have not had any problems. Should I consider changing the footwear if I start increasing the mileage?