4wd issues

[jakewalter]

I picked up a 04 Sierra ½ ton 4wd with 97k. I really like the truck and of course I found a few things that need to be addressed. The one thing that’s got me puzzled is the four wheel drive system. I knew that I had to pull the transfer case out to install one of those plates before I experience the (pump rub) that you here so much about but the four wheel drive doesn’t seem to be working right so I jacked it up to see if I could find why. I first thought the actuator on the front differential was bad because sometimes the front driveshaft would turn and not the front wheels and some times they would. The other thing that I thought was weird was that sometimes in 2wd the front driveshaft would spin. Oddly enough the service 4wd notification has not come on.
It kind of makes me think that there maybe more than one thing going wrong. I found a receipt from where the PO recently had all the fluids change and they appear to be clean and at the proper levels.
I would really appreciate some direction.
Thanks so much,
Jake

[WestButteTruck]

Yeah, at least one wheel should spin while on the lift if the actuator is working. But, there were also issues with the 4WD switches going bad, just not sure what years, but I believe 04 was one of them.