I have a job interview tomorrow. What to wear?

I have an interview tomorrow at a diesel parts warehouse for a Parts Clerk/Delivery Driver position. Now, in past interviews, I've literally showed up in a T shirt and shorts and got the job. But since the competition is tough out there, I'd be brainless to try that now. I have two outfits to choose from: a pair of dark wash jeans and a blue short-sleeved, collared shirt OR a nice pair of slacks, long-sleeved button-up shirt and a nice pair of shoes. For a warehouse job, which seems more suitable? I don't want to feel overdressed but I'm afraid the jeans and collared shirt will be too under-dressed. The interview is at 10 in the morning tomorrow, so I'm not about to go shopping for a new outfit. I hate shopping anyway. I think either outfit would be appropriate, but I don't want to feel overdressed and feel awkward walking through a warehouse in those uncomfortable clothes. Anyway, hope I can get some insight.