The "unlock" rocker switch to the left of the steering wheel is the clutch interlock switch. Normally, the truck cannot be started without the clutch pedal depressed. But sometimes in off-road situations, it is useful to start the truck in gear in low range. For example, if you are stalled on a steep hill, much easier to put the trans in first (low range) and turn the key. The truck will start and motor up the hill, all in one process. So, if you want to do that, hit the unlock rocker switch to allow the truck to start without the clutch pedal down.

I don't like safety crap like that so I disconnected mine. Now it will start in gear whenever I want without the switch.

It would appear that your truck is one of the later ones with the rear ABS. The ABS is unrelated to the load proportioning valve as already mentioned by Nathan.

If you don't live around hilly terrain, the 4.22 gears are OK for 31s, but 4.62 gears put gearing with 31s back to the exact same as 4.22s with 28 inch tires (stock size). Way better acceleration and better mileage. You can burn your tires in the fisrt two gears nicely with the stock gearing.

I'm using 4.62s with 32" tires and get 20 mpg regardless of driving technique. I would like to go to 34s with 5.29s. I wish the 4.88 ratio was available for the 8" front diff, as it would be better than the 5.29s for use with 33s.

Don't sell that truck. The V6 pickup (either Mighty Max or D50, they are identical) is very rare and an awesome truck. You won't find a better, stronger small 4x4 pickup than that. Far better than any comparable toyota or nissan. You are now among the elite, get that thing dialed in and keep it for the rest of its useful life.