Have a question about the glow plugs. I saw on here there was a TSB about the glow plugs. And I wanted to know what are the tell tale signs the glow plugs are going out. On my truck the light on the dash stays on longer. It used to just take a few seconds. Now Its almost double the time. And I always get a puff of smoke when I start the truck when its cold. Any help would be appreciated. Thanks in advance.