Ford 7.3L Power Stroke (1999-2003) :: 4WD Does Not Work / No Vacuum Leak Signs

In the past, I've had the common issues of vacuum leaks causing issues as evident from the defrost/ac and then finding busted vacuum lines. Changed out and everything fine for a few years. Now, i dont have 4wd but i dont have the tell tale vacuum leak signs. Also, even if i manually engage the hubs, still no 4wd.

I try to listen for the transfer case to engage when i switch from 2wd to 4wd, I think I hear it engaging, but to be honest the 7.3 makes so much racket Im not positive that Im hearing it, or at least not hearing it the way I "think" that i heard it in the past. I seem to recall a distinctive clunk when engaging, now its barely audible if at all. Now when I switch to 4-Low, there is the distinctive sound, and it does goes into low drive, just that its only 2wd-low, still no front wheel action.

I have never had any issues before other than the vacuum leaks, have never had reason to dig into the transfer case for any reason. The only time it has ever been touched was last summer when i had the BTS installed and all they did was remove and replace.

Do I finally need to either rebuild or replace my hubs? Is it possible not to have 4wd even with hubs manually engaged? Or is there an issue with the t-case? Or is there something else going on? I have access to a lift to attempt "driving" while all wheels off the ground, its just not mine and its a tight fit and a pain to get my truck on it.