My 96 T100 SR5 needs adjustment to the gear selector - I have to really work it to get it in Park. Its not just the light on the dashboard - it does not engage the parking pawl. Last week I found it rolling slowly as I was getting out.

Is this easy to adjust underneath at the trans or is it buried behind the steering column?

It's located in the engine bay by the firewall. It's pretty easy to git to and adjust. If yer in the rust belt, you might want to hit those threads with some rust penetrant... <img src="/forums/images/graemlins/smile.gif" alt="" />

Just to mention one possible thing to check - I'm not familiar with the T100, but on some other Toyotas, if there's too much grease that's been pressurized into one or both of the driveshafts' grease zerks at the slip yoke, then it'll physically skew the transmission forward or back enough to cause the exact same symptom that you're describing. It's easy to check for that problem - just use a small screwdriver to press on the tip of the drive shaft grease zerks. Have a shop towel available. See if tons of grease wants to come out and the transmission position changes.

Will the grease issue still happen with a 4x4 transfer case?

Yes, as long as you still have a slip yoke. Either front or rear driveshaft slip yokes (or both) could be overfilled with grease. It happened to me years ago from a Jiffy Lube or Grease Monkey, and I've heard the same symptoms and same cause from others on Toyota forums.

It isn't a "given", but it's a possibility.