kris_olof said

Start with an angry phone call or visit to the dealer that did the work last time.  There is no good reason that a rear pinion should be going out under 200k miles and zero reason to go out twice.  My thinking is there is an issue with the housing and it should be swapped.  If anything this might mean its time to make your move on that 75 you were dreaming of.  

I did call the dealer. They basically told me that the 2 year unlimited miles warranty they offer on all their work is the best in the industry, and since I am past my 2 years, I'm out of luck on this one. They did say that if I wanted to pay them to look at it, they would try to see why it is failing, but reminded me the chance of getting them to cover any repairs is very slim. I said no thanks!

The '75 is still going to happen, but it is probably a year or two out. For now I am looking at my options to fix it (hopefully with a locker) without breaking my small piggy bank. 

The cheapest option is to repair my OEM axle, but I don't trust it to live very long. I could get a used F150 axle with the e-locker, but they are going for $1,800 to $2,000. The F250 Super Duty axle is a full floater and is around $1,100 open or $1,400 with an e-locker. I would also need new wheels since it is an 8 lug, and some minor fab work to make it fit. I would also need to put wheel adapters on the front if I don't want to run mismatched wheel bolt patterns front and rear. I know a Super Duty front axle would fix the wheel bolt pattern problem, but unless someone is willing to donate a front axle, steering set up and some fab work, that puts it way out of my budget. I'm leaning towards the Super Duty axle with locker, but I have not been able to find the specs for the flange to flange width to see if it is close enough to work.

I've got to make a decision soon though, I doubt my diff is going to survive much longer.

Thanks Kris, I'll give them a call. You are right, the fact that I may only keep the truck one or two more years is part of my decision difficulty. If I was keeping it long term I would go with the Super Duty set up without question, but it is a lot more work. I have 3.73's now.