4x4Ford, I am running 37's on my truck and ran for 6 years on 35's. I ran the 35's with stock gears and I bit the bullet and regeared for the 37's. Looking back, I wish I would have regeared the 35's. Will the truck handle running 35's on the stock 3.73's, sure. Just keep in mind that you have to adjust your max towing by an appropriate amount (about a 30% reduction). If you are currently running 3.55 gears, you need to drop it by 40% roughly.
Just keep in mind that what you are going to experience is that around town, you are really going ot have to get into the gas to get the truck rolling (especially with the 4.6L motor you have). So, your in town mileage is going to suck. No way around that. On the highway, you will see it get better, but you will need to get the RPMs up to over 1800 RPM. With 35's, you are looking at getting the truck up to about 65 mph as I recall. Then you will be just entering the efficiency/power band of the motor. You drive the truck under 1800 RPM and you can plan on your mileage reflecting how far from 1800 RPM you are.
To put thing into perspective and give you some real world numbers to toss around in your head. In stock form, my truck was pulling 16-18 mpg on the highway. Installing the tires/lift and not recalibrating the speedo, my mileage fell to around 13 mpg on the same drives (loss of about 4 mpg even taking the speedo error into account). I then recalibrated the speedo (on my 97 it is easy, on your 2000, you will have to get a box that you will have to wire into the electronics of the truck) and I gained 2 mpg back (so, then was pulling about 15 mpg). In town, I was in single digits easy, regardless of the speedo being recalibrated or not.
When I stepped up to the 37's, I regeared with 4.56 gears which restored the truck to essentially a stock setup with 3.73 gears and 30" tires (ie, same RPM for a given gear at a given speed). My mileage is now 13 mpg regardless of where I drive. This also restored my ability to tow heavier things.
LIfting a truck and regearing are completely independent things. The only thing that ties the two together is the tires. You could install a 20" lift and run the stock tires and the need to regear is not needed. Truck may look a little funny, but, that is a different argument all together. The amount of lift and the need to regear is a function of the size tires you plan on running.
If you have any questions, let me know. I can feed a lot of information your way.
