Its starting to get colder and when I start my truck in the mornings I get black grey to black smoke coming out of my exhaust which goes away after warming up and if I start driving before its fully warmed up when I shift into second gear it starts shuddering which it works though in a few seconds then the gear is good acts like its not getting the air or not preforming properly but once the truck is warm it runs like a tank any idea on what could be wrong spark plugs, carb, choke pull off???