The SM465's fourth gear and the THM400's third gear are both 1.00:1, so unless you plan on rock crawling with its low first gear, why is this considered an upgrade?
Answer to your question is i don't know. Who mentioned uograge? I did the swap for a few reasons. First was I had accumulated all the stuff for anothe project that didn't happen. Second was for my 14 year old to learn how to drive a stick, he did and 3rd, it does cut a few hundred RPM off the top since the 400 has a non lockup converter.
Other folks who have done the swap really liked it. Said the 6.2 worked much better. I would have to disagree. I also have Ranger Torque Splitter that I could toss in there for OD and had planned that. Well, that 6.2 can barely move the truck along on flat ground. Adding the Ranger would only decrease power. Any overpass scrubs off speed and these small mountains here in N GA take me down to as low as 30 MPH.
Now, truth be told this truck has 4.10 gear and I ran 70 MPH the whole way except on any uphill grade. Even with the 400 (my last trip up) the grades still got me. On thing is for certain, if the truck is going to get driven on a regular basis here in GA as it does in FL, there will need to be a big jump in power. I love my 6.2s but they can't make the cut here. Turbo 6.5? Fuel injected 454? Not sure.