[Russell]

Just keep in mind that the gear spacing on the NV4500 is less than ideal. I'd sooner rebuild an NV3500 and continue to run it in a DD than to install an NV4500. I've put plenty of miles on 3500s in the past, and never had a lot of trouble. Only one I've ever had fail on me was the transmission in my old 96. The PO had it rebuilt shortly before I purchased it and filled it with 80w90. The transmission uses a 5w30 weight oil with an additive package, so it started making bad noises soon after I brought it home. Made noises for a good year / 10 000 miles before the syncronizers finally packed it in prompting a rebuild.

If you decide you do want to make the swap, it is more straight forward than you might be thinking. Most NV3500s are indeed 27 spline instead of 32 spline, but not all of them. I have an NV3500 from a 04, and it is definitely 32 spline. The shifter is in the same location as the NV4500, and both transmissions are nearly identical in length. Both use the same switch for the reverse lights, and if you purchase an internal slave NV4500, it uses the same master and internal slave cylinders as the NV3500 does. The clutch spline count is the same, as is the depth of the pilot bushing penetration by the input shaft.