Oil gauge drops lose pressure, ideas?

I just purchased a 2006 ram 1500 big horn
edition, test drove it, looked it over, seller told
me what was fixed.what wasnt like the
cluster and one side of motor mounts,
seemed fine. Driving home oil gauge drops
out lose some power, pulled over, checked oil
was fine, continue home does it twice more.
Its not leaking anything, not smoking etc. Put
my codw scanner on it and throwing codes
for misfire and egr valve. BY ANY CHANCE
would you know if those codes would cause
it to drop power or if oil gauge being bad
would? Any,info I would appreciate!! Causing
a.huge.fight with boyfriend!!
placed oil pump, timing chain, water pump,
thermostat, gas pedal system, rebuilt
transmission, brake pads and rotors, new
lower valance on front bumper and fog light
bracket on pass side from hitting a dog, new
back driver door and body work from there
back past new fender flare due to deer
running full tilt into the side of me. Some of
the old plastic timing chain pieces fell into
the oil pan and may get stuck on the oil
pickup tube. Replaced those with metal ones