Have tried almost all 4X4 fixes...now i have no forward or reverse

My 4WD has worked flawlessly on my 02 Trailblazer LTZ (133,000 miles) up until a week ago. During a snowstorm that dropped 30" on Northern MN I had a complete failure of all systems. I selected 4WD LO while at a stop and I heard a clunk. After that I had no forward or reverse. I have been helped by the tremendous brainwealth on this thread over the years but this is my first post for help. First, I unplugged the #8 fuse and waited 30 sec...nothing. Then, I had it towed to my local mechanic. I purchased a TCCM from an 03 without any change. My shop in th mean time got my 2wd working again. I installed a new front axle actuator, encoder motor and today a new front axle disconnect. My shop called today and said he was driving my vehicle to check if everything was working after the disconnect install....it seemed to only be in 2wd and then HE lost everything....no forward or reverse...the same thing that happened to me initially. He also changed my fluid in the front diff today with Mobil 1 75w-90. I am at a loss as to where I go from here. My mechanic also tried a spare selector switch he had with no result. Now the indicator lights flash instead of going solid. Should I take it to a tranny shop? One other thing I noticed both when it originally happened and now is that when I try and put the selector in park slowly I can hear gears grinding. Jim