Rough and backfires
 

Sometimes lately when I start my 1998 Chevy 2500 after it's been sitting either overnight or for a part of the day, it runs real rough and will even backfire, and then after a few minutes it runs perfect. Any ideas why?

I would do a fuel pressure check when doing a cold start. The fuel might be bleeding part into the tank when sitting. It could be the check valve in the fuel pump assembly.