Hi Guys-
I've got an '01 SCrew 5.4, 4R70W, 3.55 LS...

I put on an enormous amount of miles traveling highways and interstates at 65-80 mph, but mostly at 75-80. With the 3.55s, I'm running at 2200 rpms or so in the 75-80 mph range, and the truck really doesn't have any power in OD. This causes me to be in 3rd gear a lot, because I'm traveling in South Dakota and Wyoming, where you're always driving uphill into a 40 mph head wind, no matter which direction you're going.

I've searched and read a bunch of posts, so I know some of the torque converter/stall speed/performance questions have been beaten to death. But I'm wondering about one thing in particular that I couldn't find the answer to: How, if at all, would a higher or lower stall converter than stock (which I gather is around 2200rpm stall for the 5.4/3.55) affect my truck at highway speeds? Power? Mileage?

As we all know, there are a pile of different converters out there -- from the factory 'updated' and Merc. Marauder TCs, to lower-stall "towing" converters, to $1500 billet, gold-plated models with a built-in DVD or whatever. Mine needs replacing, and I'm wondering if I can see an improvement in the power and/or mileage with a different converter...

Thanks & sorry about the long post.

 

I could be wrong... but I'm pretty sure your torque converter is locked-up at highway speeds. So the higher stall speed you mention won't really affetct it - it's more of a launch item at startup.

I think gears will give you what you are looking for - higher RPM at highway speeds.

I've got 4.10s with street tires (285/60R18) and I'm turning about 400 - 500 rpm more than you at those speeds.

When my blower belt broke (so it was just running like a stock truck with no blower) I noticed that my truck downshifted much less often on minor grades, and was just more enjoyable to drive versus my previous setup with 3.31 gears.

You may burn a little more fuel at higher speeds, though. But to be honest, even with the blower and the gears, when I drive NORMAL/SLOW my MPG isn't really that far off from where I was with the factory setup (around 14 - 15 mpg or so). Unfortunately, it's rare that I drive at slow speeds these days...

These trucks get crappy mileage no matter what

 

Yeah what he said

And those trucks have 1500-1800 stall converters in them. The 5.4's get the lowest stall 4r70w converter built. The 4.2's get the highest and the 4.6's are in the middle.
They are lockup converters so fuel economy doesn't change much by changing converters except around town.
Alan