I've used Dodge 4x4s for plowing snow for years, I only remember using 4x4 lo lock 1 time, and I think that was to see what it did!
The last full size truck had a sure grip rear axle, in 4x4, it was a beast! I believe I could have pulled trains around in 4x4 lock!
My 4x4 Dakota has 2wd, 4x4, and 4x4 lock. To me it feels like 4x4 lock in either 4x4 position.
The 4x4 shifters tend to get a little stiff because of lack of use. Usually a good cleaning and fresh grease does wonders for them. It will be interesting to see if there are any rebuild kits available, but I suspect you can get whatever individual parts you might need through
www.mcmastercarr.com Gene