Are we talking diesels ??
My F350 diesel owner's manual states to let the beast warm up for a few minutes before putting it in gear and I do. And I ALWAYS let it idle while I hitch up in the morning. No way will I make a cold motor pull my 9000 pound truck and 14,000 pound rig up the ramp and onto the interstate.
If a turbo motor, you will want to let it idle for several minutes before you shut it down after you pull off the highway. This is important.
Highway driving is generally better (and easier) for an engine then running around town. It gets up to operating temp and stays there for long periods of time. This burns off all the deposits and also water vapor that is generated during the combustion process. Cold engines don't do a very good job of this. Short trips of less then 5 miles are really hard on engines.
Don't need to change oil early - change it at the mileage specified in your owner's manual.
