I think it's a real good idea to periodically remove the skid plates (and
other bolted things underneath) and give 'em a little wire-brushing, then
put 'em back with some anti-seize on the threads.  Actually, I replaced the
bolts with 316 stainless bolts besides the anti-sieze compound on the
threads.  It would be good to have a look at the underside of the engine
with the skid-plates removed just to see if there's anything that needs
attention.  Just a suggestion based on trying to deal with frozen bolts in
the past.  
Mind if I ask why are you dealing with the fuel filter?  The reason I ask
is that I have yet to replace the truck's fuel filter.  This was based on a
time I replaced a fuel filter on the GTS years ago and curious, put the old
filter in the sun here in So Cal one summer.  A week later of heat on it I
carefully sawed it open to inspect the filter element and observed that it
was clean.  Of course I'm not suggesting anything but what I discovered and
since then wondered about when and if fuel filters do get clogged, and by
what.  I know that there's a filter system in the take up line at gas
stations.  There's a filter in some gas tanks, so what would get into the
fuel filter?  Logically the answer would be rust and scale, with dirt
further down the list, but in reality, is this true?  Any info would be
greatly appreciated from any and all.  Always trying to learn something
new.