Grinding from tranny/tcase

So when I got the XJ I was told the tcase was probably bad. It wouldn't drive. When I would put it into drive it would go a foot before something happened and I would get a grinding noise. So I pulled the rear shaft off to try it with out a load. Put it into drive gave it a little gas(bout 1500rpm) and bam, I would get the same thing. So I put a new tcase in. left the rear shaft off put in into drive and gave it some gas(went to 3000rpm fine). I let off the gas a let it idle for a minute. Put it back in park and as soon as I did that I got just the slightest grinding noise. What the hell is causing this??? I'm going to check my tranny linkage. How do I properly adjust that if it needs it? Would low tranny fluid cause this grinding to happen?
Sorry this is long. Any help would be great.

anyone, I want to drive this thing today.

I got it. I just through the rear ds in there and drove it. Worked fine. Guess I shouldn't second guess my work. I do how ever have to adjust the tcase linkage.