You could have a Dana 135, or a Dana 150s. I lost the third member at about 30K, and it went south very fast. It started making noise under acceleration, and I got under it to check the drive line, and found a noticeable up and down shake at the pinion. Called Ford Dealer for a check, and drove over. Went to take the service manager for a ride to listen to the noise. We were going around the block, and we were afraid we were not going to make it. When I picked the MH up, he told me they have had about 1/3 failure rate on the big Dana rear members. Dana was covering the costs for the replacements.
So, yes they do fail. If it is making noise, it may fail very quickly. I have raced and done this type of work all of my life. Not much can be put over on me anymore. I hope.