[Red90]

1.2 flatland, 1.4 hills and mountains

This is why there are 5 gears.... You can choose..... Needing to shift to 4th is not a reason to change final drive ratios.

There should be two tests.

1) Can you start on a "normal" hill in 1st without undue clutch slippage?

2) Can you use 5th on a flat road?

 

[Red90]

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roamerdrive.com

 

[Red90]

I took the Roamerdrive unit out 3 years ago. I failed in catastrophic fashion the first time, leaving me stranded on the roadside. They claimed my driving style and having a chipped ECU did the damage. Truth, I drive my truck like an old man... it's a diesel truck, not a race car. There is no way that a small amount of additional power is going to create issues when driven 99.9% on road, under minimal load without towing. It's their way of getting out of warranty.

Reading your earlier post, you were using it in gears other than 5th. That is probably a lot of your issue. When you leave it engaged and shift the main box down, you hugely inclrease the load on the overdrive.