I haven't run a timed 1 mile since high school, which was a 5:53. In the Marines I did 3 miles in 17:33, a half marathon in 1:36 and a full marathon in 3:55. Earlier this year I did a half marathon in 1:59 with my bro, i'm not as fast as I was but i'm still in shape.
How is your 1 mile (5'53) more time then 3 miles( 5'51Per mile)?...............Maybe you are mistaken on the 3 mile, cause my friend does a 3 mile in 17'25, same ball park, but his single mile time is 5'05.
my mile in highschool was 5'45 and i did a 3 mile in 19 min,
recently did a marathon, got spanked of course, at over 200 less then 6% bodyfat, 4'20min

just happy to have completed it, my legs were so sore.