2003 Silverado 4.3 Misfire

[msm20032003]

I have a 2003 Silverado 4.3 V-6 with 93,000 miles on it. I have been experiencing a misfire on warm starts for a few weeks. If I would go out and start the truck within an hour or so of driving it last, it would misifre for a minute or two and then suddenly quit. It did this almost every time, but every now and then it won't. It never misfired on a cold start until the other day. I started it in the moring and it ran fine for about a minute and then misfired for about 5 minutes and then suddenly quit. This is the only time it has done that.

 

I took it to a dealer and they of course cannot get it to misfire. They wanted me to come pick it up. I had to tell them to scan for codes. They said it was misfiring on one side (1,3,5). They didn't seem to eager to look for the problem so I don't have much confidence in their ability to find it. Does anyone have any ideas on what could be going on?