2002 F-150 difficult to crank

I have a 2002 F150 SuperCrew with 5.4L V8 and 88,000 miles. The engine is stock except for a K&N FIPKII that was added 2 years ago. Recently the truck has been difficult to crank after sitting for some time. It seems that the cold weather makes it worse, but that may just be coincidence that he problem has started as winter approached. The truck is turning over just fine, but is hesitant to start. Once started, I can turn the truck off and restart without any problems. The other day, when it was very cold, the truck took a while to start as usual, but this time there was a very strong smell of gas in the air. When the truck cranked it had a very rough idle for 5 seconds or so where it acted like it was going to stall. The truck does not miss, hesitate, or operate poorly once started. The battery was replaced 3 months back, fuel filter 5 months back, and spark plugs changed at 65,000 miles. Thanks.