ive got a 2000 4.3, are you talking about the send and return fuel lines from the gas tank to the fuel filter? or do you mean all the way to the fuel rails?

from the back of the gas tank there are a couple of clips you have to disconnect, and remove from the side of the gas tank. and of course disconnect one of the lines from the fuel filter.

im not to sure how to do it from the fuel rail. ive never located mine on my 00 4.3. but i guess just try and follow the lines all the way to the fuel rail from under the truck