Depends on the truck. For the 90's magnum injected stuff and newer, 100,000 miles is not that much. In my 99 2500 with the cummins, I just did the oil change for the winter and run 5w-40 rotella t6 synthetic. Truck has just shy of 240,000 miles on it and hot oil pressure at idle is great. Synthetic 5w-40 is what the owners manual specifies for our winter temps.

The old carbed 4.2 that was(before I yanked it out) in my 88 jeep had low oil pressure. Oil pressure was so low at a warm idle that one lifter would bleed down. Get a little warmer and a second would bleed down. Even in the dead cold of a manitoba winter. Kind of embarrassing at the drive through getting coffee with this thing clacking away like there were elves with hammers inside the engine! Still went 4x4ing with it like that and gave that engine even more abuse. I tried dumping in some thicker oil, it made no difference lifters bled down just like before. After the transmission crapped out I finally pulled that engine!

With you being in the south and not having cold winters like here, I would just run the 10w-30 year round and be done with it.