1989 Chevy K2500 4x4 Problem

Hi, this is my 1st post here and I hope someone can help me out with a problem that just started with my truck. I have searched the forums and have not found anything similar to my problem.

The truck is an '89 Chevy K2500, V-8, overdrive auto transmission, manual floor shift for the transfer case with 4x4 indicator light on the t-case shifter console.

Recently while driving on a snow covered road I went to shift it into 4x4 from the 2H position to the 4H position. No matter how hard I pulled on the shifter, it would not move from 2H. I had to stop the truck and then it went into 4H with some effort in pulling the shifter. The 4x4 indicator then lit up and the axle engaged as evidenced that it was pulling in the snow. This never happened before. Up until now, it has shifted properly at road speeds since the truck was new. Now it happens all the time. I do not operate it in 4x4 on hard surface roads unless they are snow covered.

The second part of the problem is that when it is in 4H and the vehicle is moving, I can easily move the shifter back into 2H from the 4H position but the front axle stays engaged (again it's evident that it is pulling) and the 4x4 indicator will stay lit up. If I come to a stop or slow down to about 5-10 mph, the front axle will disengage and indicator light will go out. If I am stopped while in 4H and I shift it to 2H, it will function normally.

There does not seem to be any problem in shifting into 4L and back out to 4H when the vehicle is stationary. 4L works properly as it always has.

I checked the manual shifter linkage from the shifter to the t-case and it is free and not binding or damaged.

The truck is not modified and is bone stock the way it was built.

Can someone get me pointed in the right direction to diagnose and repair it. I really don't want to take it to a dealer.

First thing to check is fluid level. I would change the fluid unless it has been done recently.

I have a 90 K1500 with the New Process 241C transfer case. To shift it from 2WD High to 4WD High, the shift fork moves a syncro that locks the drive gear to main shaft. If the issue is internal, it could be syncro, shifting fork, shifting fork pads or rail.

How is the fluid level? How long since it was last changed?

//2000CAYukon

The fluid in the transfer case is the correct fluid and the level is full. It was changed out about 6000 miles ago.

I am having similar problem as well. I can only engage 4h if I put it in neutral. Then it all seems to engage. I checked fluid, she was full. But VERY dirty. I got my 89 used, with no real record of service history. So the fluid is where I started. Changed fluid AND filter. Still having problem.