rear end whine (new to me van)

[BadSaver]

Think I'd go for it...

3.73 is about a 10% increase in RPM (over 3.42). In "D"rive the transmission has a 1 to 1 gear ratio. Basically a straight shot through (This is why you tow in Drive) the transmission. There are many online gear ratio calculators. I think you'll lose about 1 mpg highway...

https://www.summitracing.com/expertadviceandnews/calcsandtools/gear-ratio-calculator

You want to solve for RPM.
This is off the top of my head - given you have a 4L65e...

 

[Ballenxj]

And if you liked the old ratio better for whatever reason, you also have the option of getting a taller tire to get back to close to the original.
The gear ratio BadSaver posted has that calculation ability as well.