Treadmill workout suggestions

switch313

So I've been working out and logging my calories for almost 60 days now. For the first 40 days or so I would alternate running days with a lifting day, never taking a day of rest because I figured each different body part was engaged and I could recover sufficiently. Anyway, I worked my way up from running a mile to running 3+ every time now. Currently I take one rest day a week because I realized I needed it and my runs have really improved because of it (as in I wasn't feeling burnt out for the duration of the run). Anyway, I'm still fairly slow 5-6 mph pace on my runs, but am starting to grow bored of the runs. I noticed when I play around with the incline/speed during the runs the time passes by faster as I'm hitting many smaller goals.. so does anyone have any treadmill workout suggestions? Some HIIT stuff maybe? I do prefer running indoors because then I can run without my shirt on (haven't come up with a good solution to nipples being chaffed :P)

Thanks in Advance