UPDATE
Replaced the coolant temp. sensor, no change.

The temp. gauge does move from dead cold position up to 140 Degrees, but never any higher. Pretty sure it was doing that anyway prior to changing the temp. sensor....
Also at the same time replaced both batteries for different reason.
What's even more interesting is that even with new batteries and after driving around for a couple of days there's still a second or two delay from crank to firing up.
When the truck was bought months ago none of these problems existed.
Still hoping to find out what causing the high idle.