I thought "oil stabilizer" was just a Lucas thing, I didn't know that anyone else made such a thing. Like the Lucas, it appears that the Shell version doesn't have any additives (at least nothing that shows up).
As for long periods of idling in heat, I've never seen an issue with my heavy duty diesels with 10W30 over the past several years. Although, I always bump the idle up to the highest rpm I can. I idle my Detroit at the max of 900 rpm as is recommended. I don't know if you guys with the pickup trucks have that option or not.
I used Lucas for over 900,000 miles in my N14 Cummins and my oil reports looked just like yours after 18-20k miles. I know now it wasn't necessary but with my Pittsburgh Power programmer adding a bunch of power/torque, I felt better adding LOS. It was only $10/gallon back then and the engine didn't suffer, other than extra fuel consumption.