95 Concorde cranks/won't turnover

I have a 95 Concorde with the 3.5L engine. During the winter I had some problems where the car would crank, but it wouldn't fire. I'm looking for any ideas of what to look at. It seemed like anytime I got the car into a warm garage it would end up firing. I've replaced the igintion coil, wires, plugs, upstream oxygen sensors and even more to try to get the problem solved. Does anyone have any ideas? I've tried to see if it was a vacuum leak but I haven't found anything. Does anyone have any ideas?

How does it run when it fires up? The timing belt may have jumped a tooth, but it will run poorly if that is the case.