Rostan

I have looked and looked through this forum and many others to no avail. The other day we had some bad snow sorms come through and kept us covered in ice for several days. We needed some things from the store so I cranked the truck let it warm up for several minutes turned 4x4h on and head out. No error code or warnings. Get to a steep hill and notice rear tires spinning not even half way up and then check 4x4 pops up on the dash. Put it in reverse back down the hill. Thinking maybe it's cold, wait 20 minutes and try cycling through 4x4h and 4x4L check 4x4 stays on. Restart truck check 4x4 goes away. Daughter gets behind the wheel I watch from side of road. Truck is in 4x4h, rear wheels spin, front drive shift spin, front tires do not pull. We finally made it up the hill with EDL and went to town and drove home about 6 hours in all and tried again at home still no 4x4. I have zero grinding noise. Unplug vacuum iwe solenoid hoping it would help to maybe stop applying vacuum to the hub, but doesn't help anything. I'm at a complete loss here and have no idea where to go next. I haven't done a vacuum test yet but I did order a hand pump should be here in a couple of days. All I can find about iwe being bad is people saying how it wont hold vacuum and disengage from 4x4 mode But it seems to me that obviously mine is holding vacuum like it wont release it. Any help is appreciated. Thanks. The truck has automatic locking hubs but does not have 4x4A. Just low and high. When it goes into 4x4 low you can tell it's geared lower as well just no pull in front wheels.