I was going through a few guages last night online, and came across a few Rear Diff temp guages from Autometer. Would this be a waste of money for most towing/hauling situations?

 

I don't think any gauge is a waste of money but on a 91 according to your sig your way past the break in period

Seriously though I thought about that but if you regularly change the fluid every 15-20k (heavy towing) and look at what’s going on you should be fine.

 

hmmmmmm.......my semi has one(2) and a trany temp,......I think if it had a problem in the rear ends (2) there would be some other problems too..clunks and chunks??
I do look at the guage gets up to 200deg some times.....I think as long as there is oil in there and no noise you will never see a temp rise

 

Run synthetic, change it every 30k and don't worry about it.

A temp gauge on the Getrag would be a good idea.