I'd go with the 3.92 gears. I don't know how the trasmissions have changed
over the past 3 years, and how the 4.7L compares powerband wise with the
5.2L, but Dodge used a pretty tall OD in the 1997 5speeds (0.73:1) and the
5.2L engine, IMHO, does not like to run below 2000 rpm.
I have a 97 with a 5.2L that came with a 3.55 and 4spd auto (OD on this
trasmission is 0.69:1). It would tach around 1750 rpm @ 60 and was a DOG in
overdrive at highway speeds. My truck also came with the tire and handling
package with 235R70-15 tires on it. I just had a 4.10 "posi-traction"
rearend installed in mine, and it made all the difference in the world. I
now tach a little over 2000 rpm @ 60 (needls sits between the 2000 and 2125
marks) and you can feel the truck want to go when you slightly depress the
gas pedal. It really hauls a$$ around 70 to 75 :^).
One thing you can do is go find a similar truck to what you're purchasing
with a 3.55 in it and get it out and up to 60mph in 5th and see what the
tach reads. To figure how it would look using a 3.92 rearend, take the
3.55 tach reading at 60 and multiply it by the following factor (3.92/3.55)
and that should tell you how many more rpms you'll pull by going the lower
geared (higher numerical number) rearend. As you recall, my truck was about
1750 @ 60mph with a 3.55, so 1750 x 4.10/3.55 = 2021 @ 60mph which agrees
with my tach now that I've went to the 4.10.
Hope this helps. I also posted a way to calculate rpms a few days ago and
Bernd has a spreadsheet that does the same.
Mike
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