sorry to drag up an older thread, but this issue is something I'm wondering about presently. I'm planning a Gryphon purchase, and larger tires as well. With my stock 3.55 gear ratio some people are telling me 35's are too tall and my tranny life will be reduced along with a loss of power. Can a custom tune accommodate this, as in more torque and possibly firmer shifts/less slippage? I'd be interested to hear your thoughts on this.

Custo tunes can help alot with firmness and shifting but in certain circumstances such as larger wheels the first step I'd take is regearing to 4.10 or 4.56. The other step I'd take is doing this valve body modification. Like these:http://www.troyerperformance.com/cgi...on%3BAutomatic
Then I would proceed to a custom tune.
JMHO

Lars is right on, Dave. A programmer is not going to give you much at all with 35" tires and 3.55 gears. I really think 4.10 gears are the way to go with those tires. The shift kit would be fine, but I'd get the gears first. (And, if you have 4WD, you need gears for both the front and back). It may get a bit expensive.

- Jack

hmm, I traded a few emails with Bill yesterday and he didn't seem to feel it was going to be a big deal. I'll have to see for myself when I get it all together.

Just for reference, what Dave is talking about is a discussion I had with him about gears and tires. As I explained to him, our Expedition runs a 3.31 gear and we have 285/75-17 tires which come out to about 33". If you do the math, it's really close to a 3.55 with 35" tires, as far as RPM/MPH goes. We haven't had any problem form our Expy, which not only is undergeared, but also weighs more than the average F-150 and in fact I can stomp just about any F-150 in the area while breaking the tires loose from a dead stop.

What many folks forget is that the PCM operates on a load-based strategy. The higher the load, the more power it will allow the engine to make. This is why 4.88 geared trucks often fall short in performance when compared to 4.10 or 3.73 geared counterparts.

Thanks Bill

Over the next few weeks my bone stock FX4 is getting a lift, 35's and Gryphon, I'm pretty excited!