My back has never hurt so much as since I started running on a treadmill.
If you can hit a track, they are often made with rubber in them now. I love running outside. I feel I get more benefit and less negatives. Pavement kills me too, though. I run on either a track (bore me to death, but easy measuring time and distance) or dirt, undulating trails.
I just found out the other day that I have pretty bad arthritis in my lower back. I gotta keep those glutes(tight) hammies(tight) and calves(not quite as tight) stretched out or the pain can reach unbearable.
Keep it up Frankenstein!