CSFI fuel pressure question

hello- i have a question on fuel pressure on my 98 Silverado K2500 w/5.7, CSFI. i am experiencing missing when at light throttle cruising at
hwy speed. starts fine. idles pretty smooth. i am thinking low fuel pressure in my regulator. i know the spec is 60-65 psi, could my below values be causing issues?
key on engine off - 62 psi when pump is running for the 2 seconds, then drops to 56 psi when pump stops.
engine running at idle 56 psi throttle off deceleration from highway speed (high vacuum) 52psi WOT 62 psi max
no appreciable leak down of fuel pressure after 10 minutes key off.
i haven't been able to block the fuel return to check pump terminal pressure... do you separate the return line at the engine? is it a 5/16" female fuel line fitting i have to adapt too? i assume i need to make a blanking plug.
short term fuel trim is about -3, long term -12 but varies. bank 1 and 2 Ox sensors flip high and low.
-dan Bemidji MN
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