Transfer case grinding on acceleration?

I apologize in advance for the lengthy post... Recently (4 months ago) had transfer case replaced with a refurb as well as yolk on rear drive shaft and have had no issues with it. Had Ring and pinion gears, all seals and bearings in rear differential replaced 1 month ago everything was perfectly functioning for 2 weeks. I was planning a long trip (350 miles 1 way) and decided to take it in for a tune up and all fluids topped off etc. During my trip I started hearing a low howling when accelerating similar to what I heard when rear end started going. I immediately called the mechanic who told me first I was probably hearing the humming of the new big mud/snow tires I’d had put on when rear end was being done. When I explained it was not the tires as I could hear them separately, he advised the new parts in the rear end would “make some noise until broken in” and he would look everything over once I returned since I was nearly 150 miles into my trip. Shortly after I was coasting down the mountain and when I started losing momentum at the next incline and pressed the gas I got nothing(my manual 4wd shifter had jumped to N) I called mechanic again as he also replaced the transfer case and was told the linkage was not replaced when the case was and the bushings were probably worn likely causing it to loosen. By the time I reached my destination the howling was getting extremely loud when accelerating accompanied by a grinding that felt like it was directly under my foot. Mechanic told me again my rear and front ends were fine (but I should check the gear oil in both since he didn’t with the tune up/fluid check and the rear level would have dropped as the oil made its way down the axel) he was sure it had to be the linkage causing the issue and my T-Case was likely between gears. I instantly went into panic mode since I just replaced it 4 months prior after having the previous one blow apart on the highway 4.5 hours from home. The linkage bushings were basically dry rotted so to be safe I replaced the whole thing and bushings. Followed his instructions to put shifter in 4H before tightening down etc. I checked the T-Case fluid, and it was super low as in there was about 1/2 qt in there and it takes about 2. Again, something he was paid to check and didn’t not to mention he advised the refurb case had some fluid in it when purchased so he just left it at that and didn’t check the level after installing or add any. I didn’t see any metal in the fluid when I replaced it, however, I am still getting the grinding (in 2H haven’t checked 4H or 4L). Both front and rear differential levels are good (had to add about 1/2 qt to rear). And ideas? I’m wondering if maybe the linkage wasn’t set correctly as I just read something about putting the shifter and T-Case both in 2H before tightening down linkage (he only mentioned putting the shifter in 4H). I have a 350-mile trip back home in a couple days and do not want a repeat of blowing another T-Case halfway home so I appreciate any feedback.