Merry Christmas everyone! I come, seeking advice!

97 Blazer 4.3 4X4, automatic transmission.

It's winter here, in the Pacific Northwest, and roads are covered with compact snow and ice. This morning, my girlfriend headed to work, on icy roads. Yes, she has to work Christmas day...grr. About 15 minutes after she left, I get a call to come rescue her. While on the freeway, she heard a very loud "clunk" and then lots of clunking and grinding. She limped to the next exit and pulled into a parking lot.

I went and picked her up and got her to work, only 25 minutes late...lol. On the way back, I stopped at the blazer to see if I could figure anything out. I started it up, still in 4X4 and reversed about 10 feet. Lots of grinding. Took it out of 4X4 and it rolls just fine, no grinding noise at all.

At this point, the blazer is still sitting in the parking lot. After work, I'll go get her, drop her back off at the blazer and she'll drive it home, obviously in two wheel drive.

My questions are:

1. What are the various possibilities as to what's gone wrong?
2. Of all the various possibilities, how would you recommend I trouble shoot, to narrow it down to as few possibilities as...well...possible?

Thanks for all the help and I hope everyone has a Merry Christmas! Safe and Wonderful holiday to all!!

 

If it helps, the other day, she mentioned that she thought she'd heard a slight grinding sound, while in 4X4. I'd planned on having the fluids checked AND we'd planned on not driving the blazer until then. Unfortunately, our children needed to borrow our Suburban, making it necessary for her to drive the blazer, this morning.