My initial post for a solution to a rough running 3.0L/6cyl has been somewhat resolved through the use of a 2 bottles of Lucas Engine Cleanout. I ran the first bottle through a half tank of reg fuel and then a second through a 2nd half tank and the rough idling seems to have gone away at least for now. I am now considering holding onto this truck (145k mi.) and would like to go forward with changing out the easily located fuel filter which is mounted to the truck's frame on the drivers side just north of the fuel tank. Is there any type of a shut off for the fuel line FROM the tank? Could this be a matter of NOT turning on the ignition so as to avoid turning on the fuel pump? This job looks pretty straight forward with easy access to the lines running to and from the filter itself. I was hoping to not make a huge fuel spill in my driveway. Perhaps a glass bottle will catch what comes from the line as it's removed from the old filter is all that will drain?
....This tank is HALF FULL.

Thanks again in advance.

Its going to make a mess no matter what. There should be a schrader valve (test port) on the fuel rail. You can remove the cap and press in the valve to relieve fuel pressure. Don't use a glass bottle! Get yourself a cheap drain pan which will do a mush better job catching all the run off.