I have a 1987 3/4 ton Suburban that originally had a 6.2L in it. Due to the previous owner's neglect, I recently removed that engine and installed an almost new 6.5L naturally aspirated. The engine basically began starting and running excellent, aside from the fact that it always seems to start up like it's missing on one or two cylinders. It runs better after a couple seconds and runs great after warmed up. Now that it's gotten a little colder out, I have been running into some problems starting it when it's below about 35 degrees. The engine starts up, blows thick white smoke (kinda looks like Cheech and Chong), and most recently the engine starts to surge massively for about the first minute or so. When the engine starts, it doesn't go to high idle on it's own... I have to give it a bit of pedal when it's running to get it to high idle. Lately, the engine will go up to high idle for maybe a second or two, then it starts power surging from about idle speed up to what sounds like half throttle or more. Sometimes the engine just all together stalls - in Park with no load on the engine. It does this for a minute or so, then it's fine for the most part. When I first start to drive the truck though, the throttle is VERY touchy - barely touching the go pedal throws you back in the seat almost like you're trying to do a hole shot. Again, this goes away after the engine is thoroughly warmed up. One observation that I question the meaning of is the driver's side exhaust has oily soot inside the pipe, while the passenger's side pipe has only dry soot in it. I don't know if these are signs of an injector pump going out, something with the injectors, a high idle solenoid or what the heck. Until a couple days ago, I was running straight fuel, no additives. The last tank full (40 gal) I added about 16oz of Power Services additive and the engine seems to idle smoother, but I haven't cold started it since putting in the additive. Any ideas?