Just turn the truck off for a little while before you undo the lines and you won't have too much pressure.

Beware though, chances are you'll have to replace the fuel sender ("cap") and the line going to the fuel filter as it gets rusty and the lines snap and bolts break off in the tank. Happened to me not too long ago.

88 4R, 350 V8, R150 5 speed Sold <...uot; />
97 4R, stock, daily driver
98 Sienna, kid and dog hauler, wife's ride