I run a tru trac in my tow rig. Pros- completely mechanical and basically nothing to have fail. It gives a partial rotation of one tire before locking so it's great on the road and doesnt eat tires. Cons- I cant find any.
Air lockers are great but if you get out there and the pump takes a dump, or line gets broken somehow you are open diff. I would go tru trac for your application.
Here's the issue, I have no idea where to find a detroit truetrac for the 8 inch toyota diff on a 85 pickup. Another thing, all my gearing and axles are stock on my rig I think they're 27 spline. Dont quote me if I am wrong. Is there a truetrac that'll fit right into the rear of a bone stock Toyota? Anyone that has a link to a website for a Detroit Truetrac for a stock 1985 Toyota pickup please post it! I wish Marlin offered it.