3.42 rears to 3.58

You will only be gaining 75rpm at the same road speed going from 3.42 to 3.58 gears. With that little of hp/tq you will just be hurting your MPG and not gaining anything else.

 

I have a Common set up, 12.7 13 spd 358 on 24.5 lo pro. 65 mph @. 1500 rpm. Given the noticeable difference between 358 and 370 in hills my set up. I think with the 22.5 lo pros your running it would make a noticeable difference. Question for Me is it worth the money spent? The trick for Me with the low torque is to wind it up to just above the top of max torque range, 1700 rpm on my engine, at the bottom of a hill. You probably have a newer engine with a lower rpm torque band. Either way dropping into the right gear will give the same final drive ratio results. I think dropping a full gear will put you in direct 1-1 drive( most efficient) gear on your 13 spd. If you find you need to split it down also, that’s ok. It’s the next shiftFind our the ratios on youre transmission, top 2 are .85? and final.73?, something like that anyway. I think the difference equals roughly one split. Get your numbers and watch the RPMs and you can figure out if it will make enough difference

 

So I have a 1" shorter tire than you but other than that our drivetrain is very close and I run 68mph @ 1450rpm. Have you verified your mph via gps?

 

The Mercedes motor is your problem. It may be rated at 1550,but if you put it on a dyno I doubt it’s putting out much over 1200.

 

My numbers were wrong, Correct RPMs 13.75 @ 65 mph and 1500 @ 70 mph.in top gear.Each split is about 250 rpm, so if I split it down once @ 65 mph my rpm is around 1625,

 

Doesn't really matter what you do with that Mercedes Benz motor. They just don't pull very well

 

Yep, thats pretty much exactly where Im at.