After all the feed back (thanks crash for yours too) I am definately taking it to a local shop that has always treated me fair and never screwed me in 4 years. Even with the right tools I am a little spooked at the down side of not doing it right. I'ld rather pay someone else for the head ache. As soon as Im back from Cali next week shes going in.
BTW
What kind of RPMs can I expect on the HWY at 70 with 4.10 or 3.73s? I ask becuase my exhaust is loudest around 2500 rpm so I would like to stay under that.
Thanks all!
I'm so glad I joined this bas *** forum!

 

Check this page: http://www.differentials.com/calc.html

You need to calculate your tire size and then go from there.

If you have stock 235/70/16's then your tire height is 28.95. Then enter that into the next set along with the ratio and travel speed.

4.10's at 70mph with 29 height = 2328rpm with an auto/OD.

 

i'll check and see what i'm running here in an hour or two, but it wasn't that much of a significant increase. i'm running 275/45r20's toyo proxes s/t. it helped my gas mileage out believe it or not.

 

Thanks for the great link!
I think I will go with the 3.73. That gets me at 2100 rpm at 70.

 

I have the same truck as you, and I'm going 4.10s with stock 255/7?/R16 tires, I tow around 4500 lbs. in hilly areas, 4-7% grade and the 3.55 gears make the truck feel like a turd. I don't think the 3.73 gears would really give you the best performance or economy you might be looking for. Plus the 4.10s would give you a little room to compensate for larger tires, if you so chose

The gears are sitting next to me right now, I'm just waiting for my Helm's complete Ford shop manuals to arrive, Alldata and Mitchell really show their weaknesses in areas like these should have them installed in a week or 2

 

Everyone has given great info and advice.
I am ordering 4.10's for sure. I bought a fan clutch to replace the one going out on my truck. Has anone in this post swapped to E-Fans? How much will I pay for these?

 

yeah, i did efans on my truck. for the full permacool kit, about $400. for buying the 2 fans seperate and all the stuff i needed off ebay: about $115 got a gain of about 10-15hp.

 

I've got e-fans.
They work great.