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Hi. I have an acquaintance that has an f250 xclb 4wd e4od and stock tires. He has 3.55 rears. Only mods he says he has is a chip and exhaust, no intake mods. He swears he gets 25-29mpg. I have same truck but with 4.10 . I have located a 1996 donor truck that has only 129k. It has psd, zf5 and 3.55 rears. I am thinking about buying it and swapping rears and tranny and have an xtra 7.3.
Anyone have this setup? If so, what mileage do you get and what rpms are you turning while going 65mph. Also, i do 90%that highway driving. Anyone think my acquaintance is not telling the truth? I dont want to spend the time and money for this if it is not going to get me some substantial results. Thanks
 

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I have 3.55 gears in mine and I get around 20 mpg. I'd you do a lot of highway driving they are good doing 65 I'm at roughly 2000 rpms but for towing I would stay with the 4.10 gears. If the truck is 4x4 you will have to swap front ends also
 

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Hi. Thanks for responses. I only tow about 3-4 times per year pulling my camper which weighs only 6000. I am just tired of paying 2 insurances and 2 property taxes. I'd like to only have one vehicle that does what i need.
 

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I call BS on the 29 MPG, Two F250 4x4 5-speeds, both 3.55s with stock 235/85R16s, both with 6637 intakes and stock exhaust, one ECLB, one RCLB, best we ever got was 23 in the RCLB. Usu. 19-20 mixed driving. With a downpipe and no-kitty exhaust, and a chip on Economy, I could imagine 25-26. But 29? Only if the whole trip is downhill and with the wind, and even that says maybe.
 

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Ive got 285's chip, intake, exhaust and the best ive ever gotten was 22 unloaded at 65. Rpm's about 1700
 

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BS he's not getting 29mpg. Closer to 25mpg, MAYBE... if he's driving super light, truck is in tip top shape, and he's going 55mph on the highway.

My 35's/6" truck gets 18mpg city.
 

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Thanks for the replies. I thought 29 was too good also, but wanted real world input. Thanks. Also surprised to find out only 100 or so rpm diff between 4.10 and 3.55 at 65mph.
 

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Also surprised to find out only 100 or so rpm diff between 4.10 and 3.55 at 65mph.
That's gonna also depend on wheel size and whether the PSOM is calibrated to wheel size. For two trucks with the same size wheel/calibration, the difference is gonna be more than that. The difference would be 1 - (3.55 / 4.10), or about 13.5%. So for example, with stock 235/85R15s, doing about 1850 RPM at 65 MPH with 3.55s, you'd actually be doing about 250 RPM more, or about 2100, with 4.10s.
 

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I can only speak from a repair perspective as a technician that heard stories from customers but the best I ever heard from them was 21-22, maybe 23. Usually, I heard between 17-20 and they bit*ed about getting anything under 16 (even with a trailer they expected better). But, it sounds like from what others are getting on here that 17-20 would be pretty sweet. To me, anything above 21 or 22 is bs UNLESS it's on a darn straight highway with very few hills and not one bit of wind either way. But how often does that happen? Too rarely which is why we call bs.

And yes, the rpm's should be different. I would even say more like 300-350 but if someone has calculated numbers from documentation or other factual info, go by that.
 
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