Silly old Dodge truck overdrive transmission options, anybody have any ideas?

I think I'm putting this in the right place, if I'm wrong, somebody let me know.

Anyway, I've got an old Dodge D350 with a 6bt Cummins and a 727. That's no overdrive and 3000rpm. With a 3.00 gear it feels like it's revving entirely too high for my liking at 70mph in 3rd gear. Also the fairly high ratios all through the trans make it feel pretty sluggish. I'm wondering what options are out there for a better transmission. I'd like to have at least 1 overdrive gear, hopefully high enough so I can run a slightly deeper gear in the axle and do 70 at around 2000rpm. I also want to be sturdy enough to hold up to towing an average sized car with the Cummins, room to turn the engine up a bit with a better flowing turbo and such would be nice too.

Options I've thought of: 47RH from a newer truck: as far as I can tell will require electronic control for torque converter lockup and overdrive engagement.

GM 4L80E: would again require electronic control, and also would need to find an adapater to make it work with the Cummins.

Allison 1000: Probably the most expensive option, Would require an adapter to work with the Cummins again, I believe certain versions of it already have self contained TCUs, please correct me if I'm wrong.

The sensible solution: which is a manual trans from a newer Dodge, be it an NV4500, NV5600, or G56. For all 3 I'd basically want to find a donor truck. Most things bolt up, only possible issue is frame/rail starter clearance from using the 2nd gen engine plate and starter in the older frame on the NV4500/5600.

The other transmission I've thought about is the ZF6 from a newer Ford or GM. I've heard pretty good things about this transmission, But I don't think anyone has ever put one behind a Cummins, so there would be a lot of trial and error and one-off parts I assume.

If anybody has any thoughts, let me know.

Can you use a 518OD version of the 727 behind a 6BT? I don't know.

http://www.transmissioncenter.net/SwapInformation.htm

Would you be better off adding an overdrive unit like a Gear Vendors one to your existing transmission?

In reply to 44Dwarf: I believe the 518 was used under the name 46RH starting in 1991. That's probably the cheapest and easiest option here, but I'm not sure it's the best option.

In reply to Wall-e: Last I checked The gear vendors unit they would recommend for an application such as mine is probably just as expensive as swapping to a different trans.

There are a couple of years, 94-97 or so of the overdrive automatic that can be configured to lockup and overdrive with a couple of switches.

There are medium truck transmissions, from school buses and the like, that are overdrive and hook up to the Cummins via an SAE adapter plate. That same adapter plate will also let you bolt up a Spicer 3053A overdrive from a military 2.5-ton truck, which is usually both cheap and easy to find.

The easiest answer, if you can find one, would be a Spicer or Brownlippe overdrive or under/overdrive auxiliary transmission. The last couple I picked up were under $400, but $800-1200 is more typical.

just buy something like this and be done with it. http://www.ebay.com/itm/47RH-DODGE-PERFORMANCE-REBUILT-TRANSMISSION-CONVERTER-DIESEL-1993-1995-T50-/190890798873?hash=item2c71fa6f19:g:fZQAAOSwjVVVwoUu&vxp=mtr

Just swapping to a 518 and not changing your rear end ratio would give you almost exactly the 2000rpm@70 that you mentioned. It will be hard to find a trans with a tall enough top gear that you can do that AND have more gear reduction in the rear end.

I was pretty sure I wanted an NV4500, but it looks like the 47Rh would be a lot cheaper/easier to install and it's taller 4th would probably help me more than the NV4500s shorter 1st.