This is the first vehicle that I have owned with 4WD and ABS (either one of them).

Okay first off is a pretty easy question, I just bought a 92 jimmy sle but it did not come with an owners manual. My question is: what is the correct procedure for shifting into 4wd and going into low and then back to 2wd?

The second question has to do with the ABS brakes, at first all of the dash lights were off and everything was working - even the cruise control worked. The only bad thing was that it was like driving with manual brakes, extremely stiff. After looking through the forums here, I decided to try to disconnect the ABS and just drive with normal brakes - well, it didn't work. After disconnecting each plug from the ABS unit individually and then in all combonations and finally pulling the fuse, the pedal was still very stiff every time. Next we figured that we would just change the master cylinder and got the same result. About halfway through changing the power booster a neighbor came over and showed us that it was already holding vacuum so that it was good. I don't know what to check or change next, but I am tempted to just change the wheel cyliders (or the whole caliper rather, it is easier, and it's only like $10 apiece)

Thanks for all your help folks!

4wd Hi can be engaged/disengaged when you're traveling less than 45 mph and preferably under no engine load (cruising or coasting). 4wd Lo must be engaged/disengaged at a stand still with brake applied.

As for the hard brake pedal, the ABS system will not likely be the culprit. Depending on what vehicle you've driven in the past, the Jimmy's braking can feel stiffer than others, but should not feel as though you're stepping on a manual brake. I would rethink changing out the booster, and also check the vacuum lines to it. Alternatively, check the brake proportioning valve, usually located just next to the master cylinder. Good luck!