Locking the hubs

[1969 GMC]

I actually think my owner's manual says that you CAN shift on the fly at low speeds from 2Hi/4Hi, but NEVER into low.

The newer NP205's have synchros because of the advent of auto-locking hubs. Other than that, they arent any better or worse than old ones.

Personally, I don't like shifting on the fly. I never did, either, but then my Rockwell exploded. Sooo yeah. :p

Also, alot of vehicles came from the factory with drive flanges instead of hubs in the front axle. All of these vehicles spin the front axleshafts, diff, and d-shaft constantly. I wouldnt say there is a noticeable difference in engine life, but perhaps gas mileage.
In the winter, I used to lock my hubs in at the first snow, and unlock when spring came, just shifted in and out of 4wd as needed. Worked fine for me.