We previously gave the truck a tune up. New plugs, wires, cap, rotor, cleaned the throttle body, checked the wiring and connections. Looking for loose or non grounded items. Without using a wire testor hard to tell if there are any wire breaks under the wire wrap. We have changed the coolant temp sensor, ait temp sensor and Map sensor. No codes from the computer. I have thought about the intake and or head gaskets, because the dealer once said he noticed a puff of smoke during start up. I have not actually seen this, but why would he make it up. I also thought about valve seals. But again, why only when it is cold? During the summer months it drives great. I am trying to keep the truck around because it is paid for and otherwise, nice to have for hauling. I am just finishing up my garage project and am anxious to finally get back to working on my muscle cars which have been sitting for 10 years, so I don't want to spend all my free time or money on this truck. So I am stuck because the dealer can't seem to find it without breaking my bank and the issue seems complex and above my previous attempts. But someone has to know.