96 2.2 oil bypass valve

I am trying to diagnose some low oil pressure issues on my 96 s10 2.2 4 banger. From what i can tell, the oil filter bypass valve is located behind the oil filter. The manual is a little
foggy from there. Is it pressed in? DOes it screw out? If it does screw out, what size and type of tool does it take it do it? are these available in different pressure ratings? Access is more by feel then visual.
I did change the oil pressure sender and the readings don't seems as bad. 40 psi at RPM and 18 idling. But as it heats up it drops to about 20 psi at RPM and into the red idling (less than 10? with check gage warning). Oil was just changed. I did just have the top end of the motor done due to slipped timing chain and bent valves.
And, can you change the oil pump on this without removing the motor? It seems from research a higher output oil pump was available from the earlier 2.0 that will bolt right in.
If the bottom end of the motor is sludged up a bit, could it cause this problem? (i know the top end is clear now)
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