Alright- I'm short on time tonight, so:
If it was a rear locker you installed, I suspect your viscous coupling in your transfercase has failed- allowing slippage, hence the rolling and tire spin. Or you have had a front differential failure of some kind. The AWD case parks through the front differential.
If it was a front locker, your locker could be faulty.
You may have to start looking for a transfer case, you have options though:
You can swap in a 4406 for "real" 4x4 and low range and 2x4.
I did a write up on the 4406 swap it lists all parts needed and has a how to. Link my my signature.
You can replace your 4404 with a J/y unit, check for slack in the chain. The front and rear output flanges shouldn't have much slack between them, otherwise the chain may be too stretched.
I am working on a 4404 un install and re install thread- it will be ready in a few days.
In the meantime, set your parking brake when you park. If it doesn't work, find two large rocks to carry with you
