I've got the 3.73s in my FX4 and wouldn't go anyother way. 6th gear is so high that I don't hit 2000 rpm untill nearly 75 mph. It doesn't take much for the tranny to drop to 5th with a load behind you and a higher gear wouldn't help any. If you don't want the big mirrors-wish I had them-get the FX4. Once I got used to REAL mirrors I feel a little handicapped with anything less.

 

I felt the same way about the sub, and almost talked myself out of the sony system/nav because of it. Thankfully, i found out it takes a whole 30 seconds to move/remove it, so I got the Sony and couldn't be happier.

 

Can you remove it? Didnt know that. Going to take a look now lol.

Well thats cool. Thats handy to know as it cam out so easy.

 

For those of us who do not have the truck yet...is anyone able to snap a picture of the sub removal process? Or is it really that easy?

 

It really is that easy. lol

I will take a pic in the morning with it out and in though.

 

I was wondering what the indents in the carpet were for. Is the wiring for the sub there or only with the sony setup?

 

Why? The rear diff ratio is only part of the equation. What matters is total torque multiplication between the engine's output shaft and the wheels.

6R80 1st = 4.17:1
1st * 3.73 = 15.5541
1st * 3.55 = 14.8035

2008 4 speed 1st = 2.84:1
1st * 4.10 = 11.644

Even the 3.55 with the 6 speed is better than a 4.10 with the old 4 speed.

 

That expalins fully why my truck with the 3.55ls tow's so well and gets great MPG.

 

With the larger 18" wheels go with the 3.73, otherwise the 3.55 works great with the smaller 17" wheels.

 

If you want the maximum towing, you'll need the 3.73. If you seldom tow, perhaps the 3.55 are a good choice.

 

Well my 3.55LS tows a lot better than our 2008 work truck does with 3.73's. I tow 7-8k lb almost everyday and the 3.55's have no problem at all. it's like towing 2-3k lb with an 08. But like some people have said the new 6 speeds give you a higher final drive much higher than the 08's 3.73, even if you went for the 3.15's in the 09's. But if you tow anymore than 8k lbs then 3.73's will def help but you will take a little loss on MPG but thats expected due to the extra tq.

 

I will agree with ya on that one!

 

How much larger is the tire diameter?

 

Not sure of '09s but from what I have seen from the 17s to 18s to 20s on the 04-08 stuff...no more than 2" difference, depends on the truck level and package. Mostly about an inch or so difference.

 

I'll give you my .02 worth here. I went from a 1997 F-150 5.4 w 3.55 to a 2009 F-150 3.73. The 3.55 was good for gas mileage seeing the engine rpm's were lower. The 2009 turns about the same rpm's as the 1997 did, and it does it with 6 speeds in the trans vs 4 in the 1997. I pull a 13,000lb boat so I wanted the 3.73 with the new truck. It gives me a little better pull than the 97 did. I also pull a snowmobile trailer and I could keep it, the 97, in OD while towing the snowmobile trailer without the trans downshifting and upshifting all the time. I have not pulled anything with the new one, but I am anxious to see how it pulls the boat. Of course I don't pull the boat 70mph down the road with the F-150, but if it handles it, I just might. If I go on long trip, that is what the 2003 F-350 is for. The 6L does a wonderful job.

The 3.55 gives you lower engine rpm's vs the 3.73, about 200 to be exact. If I were you, go with the 3.73 and 6 speed trans. Great combination!!!!!!