t-case in 79 1/2 ton (pretty sure its np203) will not shift correctly. I can shift it one click down (4hi-loc lights turns on), back up to n, but not any further up into the 4-low range. When I shift down from n, is it supposed to go straight to hi-loc and not 4hi? Also, any ideas about 4lo problems? It will not shift at all into 4lo or 4lo-loc.

Odds are you have a NP203 unless someones changed it out. The shift pattern for the 203 is as followed from all the way forward(towards the motor) to all the way back (towards seat)
4-Low LOCK
4-Low
Neutral
4-Hi
4-Hi LOCK

Now if you have the Mile Marker 4x2 Conversion Kit on your 203 your shift pattern is as follows.
4-Low LOCK
2-Low
Neutral
2-Hi
4-Hi LOCK

The shifters on the 203 are straight up junk. So you might need to adjust your shitfter first and go from there. If you havent already done so Id suggust going out and buy a Haynes Repair Manual (manual Number 24064.) Adjust according to the manual. If that dont fix the problem then id check your t-case fluid (if low DO NOT USE TRANSMISSON FLUID use 10w-30 or 10w-40 SE motor oil.) If that doesnt fix it then you have problems inside the Transfer case and i would suggust taking it somewhere for them to diagnose the problem. Are you utting the Transmisson (not the t-case) in neutral before you try to engage 4-low? Try that and see if that works for you, if for some reason it doesnt then start by adjusting the shifter and go from there.

Cory

how about checking the linkage from the shifter to the trans fer it will have nuts on threaded rods that will come loose

if no front driveshaft or unlockable hubs are in, the t/c will not engage 4-hi and 4-lo, only the loc positons will work. Try slamming it, i have to and ive wheeled 4 of them and all needed slamming and the tranny in neutral.