Ratio 2.53 or 3.36

2.53, you need direct drive tranny. You wont be able to spec a truck to have 600 hp/2050 torque because direct drives are capable up to 1550 and have 1750 only working top two gears. 3.36, you need an overdrive tranny. Any torque, any horsepower.

 

The question is where are you going to be running flat land Florida or high on the Rockies.

 

Need more information
Flatland hill. And. Gross. Wt

 

In PA, i have loads weight btwn 30-37k pounds and 10 speed manual direct drive, 2.53 is nailing through everything. Runs like 3.55, same rpms. Usually get 6 mpg when i drive 65@1400 rpm.

 

If you wan MPG you want direct drive transmission. Then pick how fast you want to drive. Then pick the rear end to fit that answer.

You can also pick a transmission with over drive but spec the truck to run in direct drive. So on 13 speed direct drive might be 11 or 12 gear. Then have the 13 as a true over drive to use only when you really want to go fast 70 75 like out west

 

Given the choice (dependent on application hp,tq,load etc) I will always take the DD over the OD, tranny just runs easier,less parasitic loss, less heat, less wear and tear, BUT, as stated by Russ, they will not fit every application.

Also keep in mind your max speed setting, with a DD it is easy to spin driveshaft too fast, if you are specing a new truck they will only let you go so high.

My old Pete was setup like Brandt suggested, it was a 308 rear, tall rubber, and a 10 over, I ran in 9th alot (small motor) and used 10th as a "come home empty" gear. lol

 

How fast are you planing on running, over 68?