No high gears when first started

Interesting.

Older trucks need a little time to warm through and get moving. I remember a couple that would not have much to them until they were moving about that long like a older woman. Once warmed through the jake and shifting and power etc will be normal or nearly so.

For your issue, I would take a look at your shifter, related to the high range splitter. Maybe you have some kind of blockage from moisture or something somewhere in there that goes away when it warms up. It's a total guess, a shot in the dark. A starting point.

 

How cold? Below -20°C I find any of our trucks that have sat a day or two won't shift out of low range until they've warmed up 15-20 minutes. Things don't like to work when they get really cold.

 

I had a W/star that was doing same thing but i waited till it stopped shifting when I was loaded and had to put new A/C O/rings that I had left over from fixing a/c into the slide cil. inside the back box, it will be best to fix the problem when you can use the correct parts at a time of your pick not at the time where it may cost extra $