90s had 3.73 for autos and I think 3.31s for m47. I swapped my auto for an m46 on my 93. I would have swapped in a 3.31 if I could find one with an abs tone ring. I still have not found one.

But the 3.73 works fine with the gearbox. It turns about 2500rpm at 60mph. It works really well if you drive between 35-50mph because you can keep it in overdrive.

I am not sure what the effect on fuel economy is. I had an 89 with a m47 and 3.31 and I am pretty sure my 93 with the 3.73 actually gets better fuel economy. Both were better than the 93 when it had the auto.