Any Allison Experts?

[truckster]

I know this is not a MH board, but all the smart engine/transmission people I know are on this board, so here goes:

I have an Allison AT542 behind a Cummins 5.9 in a 97 MH with a Freightliner chassis. The transmission is kind of a dog. Because it doesn't have a locking torque converter and final drive is 1:1, I have a hard time keeping it at 70-72 MPH on the freeway. The slippage in the converter is really obvious as soon as I hit even a minor grade. I don't need to go 85 MPH, but it would be nice to hold a steady 75. I've done a lot of research, and here are some options I've come up with, and I'd appreciate any input:

1. Replace the torque convertor with a BD-Power torque converter part # 1060200X. It promises 130 to 140% more torque transfer and better shifts with less heat. Cost $760 plus $300 core (refundable) plus fluid.

2. Replace the transmission with a used MT643. They're not too hard to find and the swap looks to be pretty straightforward, as long as I get the right bellhousing and flex plate. The advantage is a locking torque converter. Cost would be $800 - $1200.

3. Replace the transmission with a used 6 speed Allison. This gets into electronic controls, which can get expensive. The obvious advantages are the locking torque converter and overdrive. I would have to do wiring and computer for this one, so it would take more of an investment in time. Cost would be $2500 - $3500.

Thanks for your input!