The larger the rear end ratio, the more the eninge has to spin to turn the wheels the same speed.
A higher ratio will get you marginally faster 1/4 mile time, and the ability to pull a heavier load more easily.
BUT
A higher rear end gear will get you less gas mileage on the highway.
Honestly, there isn't much difference between a 3.55 and a 3.73.
Now if you were comparing a 2.93 and a 4.11, that would be a dramatic difference.
You may also have to consider the kind of transmission that is in the truck, 3.73's work really well with overdrives.
But honestly, the 3.55 would fare you better gas mileage in the long run.
-SF