I'm getting a rough idle and smoke when starting after the truck has sitting for awhile, like an hour or so. Once it settles down, the idle is fine. Cold starts are no problem, fires right up and idles smooth. I thought maybe air intrusion, so I replaced the return lines. Didn't seem to make a difference, but it was time for new ones anyway. Engine sounds normal, just stumbles around when started up warm. Any ideas? Thanks!