Back Pain. AGH

So, I'm having some troubles at the gym, & I'm going to work on figuring them out, starting tomorrow.

The last couple times I've tried to run or do the elliptical at the gym, my back has started killing me.  My back has been fine when running IRL. 

There has also been a shoe switch.  Shoes that were fine for running IRL are actually shot to hell & I shouldn't be wearing them.  Newer shoes w/only 100 or so miles on them are the pain ones at the gym.  Tomorrow, I will go to the park & run in the newer shoes to see if back pain follows.