Car cranks awhile before starting in cold temps

I have a 1995 Mercury Sable 3.0 automatic with 186,000 miles. Last winter, when the outside temps were cold, the car would crank awhile before starting. Probably 10 or 15 seconds. It wouldn't drag like it would if the battery was weak but it would crank awhile before turning over. I thought maybe fuel pump was getting weak but it only did it when the engine hadn't been started in awhile. This summer, when outside temps rose, it started fine. It runs fine. Last week, we had a couple of nights down in the 40's and, sure enough, it cranked awhile before it started. If I turn it off and start it, it will start right up. No one has been able to tell me what is going on. I've changed the plugs, wires, rotor cap and button, PCV valve, cleaned the IAC valve and MAF sensor elements. Do you have any ideas? Thanks for your help.