[lnfletcher]

There is really only 4 points that could be causing it to stick as I see it.
1. Steering rack.
2. Steering column.
3. Pillow bearing.
4. Knuckles.
Seems to me that the Pillow block bearing is closest to the heat sources and could be causing the sticking. You can remove it to examine it to see if it is seizing. You can get a replacement at most Tractor Supply stores fairly inexpensively.
If you can get it warmed up and duplicate it when in your shop or driveway, you can disconnect its linkage and test each section.
You didn't say how long it lasted when not running.
The column is not subject to that much heat.
The knuckles will most likely cause the steering to be uneven if they bind.
The rack is the hardest to test and most expensive to fix.

Hope this helps.