My guess is your runs outside are not at a 1% grade, but mixed  angles. Try removing the 1% and running your treadmill flat.

Pain  on the inside of the ankle can come from minor plantarflexor muscles  deep in the calf, whose tendons must wrap around the ankle...

http://www.getbodysmart.com/ap/muscularsystem/footmuscles/tibialisposterior/tutorial.html

Running  on a constant grade for a half-hour or so could be a little much for  them. Even if the grade is slight, the effect is cumulative.

A  year is not a long time to have been running. I remember the aches and  pains of my first year or so, and you have to trust your body to adjust  in time. This process is not likely to be painless. For your part, the  fundamentals of good nutrition and hydration combined with your  training, will deliver results as long as you are consistent and do not  run through your injuries. It's OK to take a little time off every now  and then to gently rehab your aching legs. Remember that tight muscles  stress tendons that may be remote to the muscle itself. Explore those  deep calf muscles for tender spots and rub them out per instructions in  this video by Dr. Jonathan Kuttner...

http://lifeafterpain.com/vault/treat-your-triggers/finding-triggers/

Whatever  you do, it's better to take on your pain directly by rubbing it than to  resort to anti-inflammatory meds. Inflammation is the process by which  your immune system repairs the wear and tear of exercise, and the pain  is what limits you from inflicting further damage on yourself. As for  the time required, some soreness goes away in days, while tendonitis and  other overuse injuries can take months. Try cutting back on your  exercise during the healing process, and if things continue to worsen,  consider suspending the exercise altogether and consulting a doctor  familiar with sports injuries.