Last time I was home I installed gauges. My fuel press gauge reads 16 psi (idle) 26 psi full load. It has been suggested that is 5 or so psi too low. As I have just changed the fuel filter, it has also been suggested that I change the overflow valve, which I will do when I get home again.
One thing I have never messed with though, is the pre-filter. Are you 'sposed to clean that? If so, how. Should I check that before buying a new overflow valve?

 

You should check the prefilter but I doubt it's the problem.
Instructions> http://dodgeram.org/tech/dsl/filter/pre-filt_clean.htm

Ignore the every 12k bit, unless you are using trashy fuel every 100k is more than enough. Even then the prefilter is likely to be spotless.
Easy way to check the OF valve is to pinch off the rubber return hose with pliers. If the pressure remains low the problem is a fuel supply restriction (filters, kinked line) or a bad lift pump not the OF valve.

http://dodgeram.info/tsb/1996/14-07-96.htm outlines diagnosing fuel pressure problems very well.