What could be the problem?

I have a hard time getting my truck started. When I first try starting it sometimes it starts right away sometimes longer, I haven't quite figured out a pattern yet. After I have drove the truck for some period of time and park it and then come back to start it say 15 minutes or so it takes a few minutes to get it started again. When it starts it has a little white smoke but nothing serious, it idles just fine no loss or power and mileage seems to stay good. I haven't replaced the lift pump or injectors and it has almost 120,000 on it. I did replace the fuel filter. I have an 05 pretty much stock besides 5" exhaust and smarty jr.