Lately I've noticed what seems like a slight engine lope when I first start my truck from a cold start. It only does it when engine is cold & goes away after truck warms up. The RPM gauge seems to move a little more than it used to at idle & it bounces some with the lope....What would cause this to happen only when engine is cold & goes away after warming up?

 

The injection pump reacts very rapidly to changes in rpm, so if one cylinder misfires or fires weak for whatever reason, by the time the next cyl or two fires, it bumps up the fueling to bring the rpm back up. Then as it over-revs from the extra fueling, it cuts fuel to bring the rpm back down.

In short if anything is out of whack it creates a rough idle. The most common issue is "pop" pressure being uneven a little. When cold this sort of thing tends to be worse since more things can affect cylinder balance. If compression is uneven, the weaker cylinders will not fire as reliably when cold due to the basic principles of compression ignition. Once hot the cylinders will fire more reliably regardless of balance, making your idle better.

Valve adjustment might smooth it out a little. Pop pressure I would be reluctant to hassle with unless it really bugged me. Some fuel system cleaner might smooth it out too. Or a tank of biodiesel, but be ready to change your fuel filter as the bio will clean all KINDS of junk out of the fuel tank and plug up the FF.