I can only chirp my 265 75 16's from a dead stop. What's the 5.9s optimal rpm range?

 

I would say 1500-2500rpm.

 

So I need to keep my average speed in that rpm range to keep it running effiecently?

 

Yeah I guess... a lot of it has to do with your driving style. If you do 4 grand shift expect ****ty mpg's compaired to 2k shifts.

A tune up also goes a long way as well. I picked up 1 mpg after I did my tune up and I was driving it harder.

 

It normally shifts bout 2200 or so. Every now and then I'll wrap it 4k or so (girls round here love loud trucks) but not usually. I'm not really worried about a little mpg loss. I get right at 14 now and I'm fixing to do my plenum and a ported tb and a tune up. I would like to stay around 12 or so if possible.

 

I know its a ford guy but it should help you under stand it better. He makes a lot of sense.

http://www.youtube.com/user/powerstr...25/m3ccAkvP1i0

 

i used some of the calculator links provided and i have a hard time beileveing that at 70mph with 35in tires and 4.88's i would be running at 3200RPM

 

That seems really steep. Hope you run the 1/8 and not the 1/4

 

You would be running 3200 if you turned the OD off. With OD on it would be 2260.

Understand that locking the OD off turns the truck into a 3 speed. That's not that surprising that rpms would be that high.

You can run a stock truck up to 5300 rpms with relative safety. Replace the valve springs with something a bit more beefy and 5500 isn't out of the realm of safety. I'd recommend hardened pushrods if your spinning higher than that.

The bottom end of the truck as manufactured is good to about 6K from what I've been reading. More than that is going to require forged internals.