Straight 9 speed

What RPM is engine turning @ 70.

 

Geez dude. How many rpms do you think your motor is capable of turning out? Fuel wont change that. You have no more gear to go any faster. Unless im reading this thread wrong

 

Um you do not have 3.36 axle gears.
You most likely have 4.36 or 4.55 ball park.
Or your final drive gearing is not .73 to 1.
Or you have direct drive trans?
I am clueless.

 

You're truck will NOT go any faster then 70mph. You have reached the engines governor at 2200rpm. In order to go faster you need an over drive transmission or to swap out rear gears to something under 3.0:1 but doing that you will loose the pulling power your truck currently has. I'd say slow her down so you're not turning much over 1800rpm on the big road or sell it and get a better suited truck for your operation.

 

Whoever told you it had 336 rears is not correct. You need to crawl under there and find a tag yourself.

Go to the road ranger site and find the road speed calculator. That will tell you what your RPMs should be for whatever Road speed you're doing for whatever rear end and transmission and tires that you have.

You should also crawl under there and find a tag on your transmission but that certainly must be a direct drive transmission.

I think @Intothesunset has it right. Your truck is geared really low.

When you find out what your rear end ratio is and you go on the road ranger site you can see what it would be with the direct transmission or with an overdrive transmission. Look at whatever speed you want to cruise at and see what the RPMs will be. I don't know if they still make them but you might even need a double Overdrive.

 

3.36's could be correct and his speedometer could be off. This is off the spicer wedsite, but sense he hasnt told us the tire size I just guessed low pros which is a 40" tire. Looks like 3.73's are a close match to what he's telling us. You guys gotta remember that most fleet trucks spec'd with a direct drive trans run low 2.xx:1 ratios and once you get to the over or double over drive trans is where you get the 3.xx:1 or lower gears.