So it's about -15 to -25 degrees during the day and when I get into the truck, it starts (not happily, but no one is at that temperature) and I let it warm up for about two to three minutes before I put it into reverse and back out of my parking spot. It goes into drive with its usual clunk (the same one every time in the automatic since day one).... now when it's frikin' cold, I hear two more clunks while I begin to move forward and the back of the truck is moving up and down slowly and in time with the speed of the truck for the first 200 feet or so. Then it stops and life continues as if nothing happened.

What the hell is wrong with the truck? 'Cause I dunno as I've never had a car do that!!

I live in a part of Canada where a LOT of salt gets used, so I'm used to squeaks and rattles and rust, what is the hopping about and why does it stop after about 200 feet and increased vehicle speed?

check your u-joints on the driveshaft.

Does it happen every time or just the first drive after sitting for an extended time?

It does happen everytime its gets really cold, (it can't hear it around zero but when it hits -12 to -15F I do) but not when the temperature goes up. The only time when it happens is when it has been sitting outdoors for the day at work. During the night it sleeps indoors in a heated garage.

How does one go about checking the u-joints?, I come from an era 'o front wheel drive cars where we have CV joints instead!

I don't have an FSM but one is one the way, could it be too much to hope that there is a procedure in it about checking the u-joints??

Makes me wonder if the low temps cause the tires to squat and then get flat spots frozen in them.

Hmm....I hadn't thought of that. I don't drive more than a few miles to work so the tires wouldn't have time to get warm. They do go from T-Shirt temperature to -500 degrees in 10 minutes and spend 9 hours outdoors in that temperature. And the "winterplus traction" tiredoes not appear to be sold in Canada anymore certainly raises my eyebrow in suspicion.