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Discussion Starter #1
I have a 97 with a zfs5 and am running about 2200-2300rpm at 65mph. I don't have much experience with anything other than general maintenance and don't have any mods on the truck except for an S&B intake. Just wondering what can be done to make the truck a little easier on the RPMs at highway speeds?
 

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All you can do is to replace the rear end gears, or go to taller tires.

I have ran my truck at those RPM's all day long without a worry

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Discussion Starter #3
Thanks. Yea, not concerned with the RPMs at 65mph, but do a decent amount of highway driving and would like to run at 70-75mph. Would that be something like swapping to a dana 60 for the rear axle?
 

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You have a Ford Sterling 10 1/4 rear end. To have a shop do a gear swap is going to be $1200+ and if your truck is a 4x4 you'll have to do the front also $$$$$$

You can go to a junkyard and find a truck that has a 3:55 rear end and swap that in.

I also drive freeways at 75 and 80 mph and have no problems with my 4:10's which is what you have

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Just remember if you have a 4x4 what you do to the rear you have to do to the front.

Just so that you know, you can hold these engines at the RPM limiter all day long with zero problems.
 

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Discussion Starter #7
Thats good to know, wasn't sure if consistent high RPM was limiting lifetime
 

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I switched my oldest to me 97 F-250 E4OD from 3.55 to 4.10 for the mountain towing I do around my house. It comes out the hole a lot better with a load in the mountains but screams ON the interstate. Except for the loss in MPG the truck is happy all day long at interstate speed 65-75. It was a little weird to me to be running the thing so hard at first, but I am happier with the performance OFF the interstate. For comparison this truck is a 97 SCLB XLT 4x4 with E4OD, 225K, Tymar intake, new up pipes into 3 inch downpipe to 4" free flow( I mean through the factory cat of course) wink wink. For the interstate and light work I use my 97 SCLB XLT 4x4 299k F-250 with E4OD and 3.55 bone stock It still turns around 2K plus at 65-75, better MPG but less hill climb power with load. In a way I wish I had just kept the first truck with the 3.55 because in all reality the notice is not really worth the money. I know this is the reverse of what you are saying but this is my side of the story. By the way both trucks run 265/75-16 I had a taller tire at first on the 1st truck 285/75-16 with 3.55 no good.
My two cents if you do any towing in the hills keep a 4:10. If you flatland interstate with no load go 3.55 if you feel it worth the money but it may not pay off for a lot of miles.
BTW I just bought a whole new rear drum to drum and intalled it. front I just changed the pumpkin. This is the easiest and cheapest way to switch the gear ratio
 

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It have a 3.55 from the factory in my '96 F250, and it sure is nice to cruise at about 60mph / 1500 RPM when pulling my 28-foot 6,000-pound travel trailer in overdrive on the highway. Of course, when I hit the hills, I punch-off overdrive to keep from losing speed or the automatic does it for me, and then downshift from there as needed to go up the mountains. I have to downshift sooner than if I had a 4.10 in the rear, but since I only "visit" the mountains and don't live there, the 3.55 works for me.

So, in my case the 3.55 diff allows the ole 7.3 to loaf at around 1500 mile-after-mile on the highway. It's quieter and seems so easy on the engine. I like it.

But if I had a 4.10, I would not spend the money to make a change. There isn't enough difference to make it worthwhile, I would think.
 
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