ok is going to be kind of long, so i will try to make it shorter. i have a 72 bronco with a 76 frame and axles. i bought another 76 with a fiberglass body. it has everything. so my plan it to swap my drivetrain and axles over. then sell the over bronco will be a good deal the body has surface rust on rear quarters going to try and sell that one. My biggest concern is i have 4.88 gears 37s and a np 435. im tired of anytime im on the highway running at 3000 to 3400 rpms depending on my speed and see my mileage go to crap. when im in town i get 14-16mpg on highway it goes awful. the other bronco has a c4 with art carr shifter. i will be doing some sort of overdrive either from a automatic or manual. which is cheaper? what can you do with automatic with overdrive in EB? which is better for wheeling? any, all advice on this is greatly appreciated. not sure what to do, love driving a standard but willing to change to automatic for ease and overdrive. thanks everyone and please write any comments, questions, concerns and opinions. Not sure what to do, i know broncos but still flustered with what to do

If I've got all my math right, you typically drive around 70-75MPH which is resulting in your 3000-3400RPMs.

Swapping that NP435 out for a ZF 5 speed should put you around 2500RPM at 75MPH while retaining the rest of your running gear.

Never done the ZF swap, but they seem pretty plentiful in the yards. ZF adapters look to run around 369-379 from the parts houses.

This would be my choice of transmission swap were I to pull the 3 speed in favor of a 5. I know there are quite a few people partial to the NV3550 and NV4500. Don't have any experience with them to speak of.

but what about the idea of keeping the automatic and what tranny to use then????

also what about the cost of the adapters and conversions for the clutch and all...... like i said i have no idea right now. minds up in the air!!!!!!!!!