I wouldn't even think about swapping the gears, but rather would swap the complete axles themselves. gears aren't as easy as bolting them in. they must be set up properly and, long story short, it's just not for the novice.
3.55s should give you more perceived power (and a bigger smile) and a bit better fuel economy (since the engine won't have to work as hard to get the truck going from a stop). :thumbsup:
I'd do it in a heartbeat. :yes: