When you changed the oil pressure sender, did you remove the intake manifold?
If you're loading up parts, bring intake gaskets. If they've never been changed, I suspect that's your issue. And if we're just going to toss parts at the car and see what sticks, they're cheap and a very common issue on those motors. I would imagine they've already been changed at 225k.
I would be very surprised if a code reader had zero live data, usually it has the bare minimum mandated by ODBII standards. I would bet it has freeze frame at a minimum. Look at ST/LT fuel trims (short/long) on the data list for the freeze frame. The combined value of the two should be +/- 10%. So -5 ST and +3 LT, would be be -2 combined, you get the idea. As I said, my assumption if they're original would be leaking intake gaskets, causing a miss especially when cold. In the example above of "-2%" fuel trim, -2% indicated the ECU is taking away 2% of expected fuel requirement at that load/rpm. Vacuum leaks mean very high positive numbers, adding fuel to compensate for the air. High negative trims means the ECU is pulling fuel from the expected volume it should deliver.
https://www.amazon.com/gp/product/B07N5ZGJ2M/?tag=atomicindus08-20
I love this little thing. ^
Had a similar vintage Taurus with p0300 a month or so ago. Vacuum leaks causing sky high fuel trims, causing misfires. Funny the ECU didn't bother flagging lean codes, but I digress. I bought that for $15 when amazon had a promo sale; and it gave me all the info I needed. Smoke machine confirmed intake manifold runner control valve seal on the intake was leaking. Sometimes I don't really need to drag out the modis/autel/pico whatever. Sometimes things are crazy and you need all 3 and pages of diagrams.
Bi-directional IMO generally starts at 800, not including the service reset stuff which as a stand alone tool without bi-directional is like 150/200ish. Manufacturer codes and data starts around the same $200. I used a launch CRP129 when I was first learning. Good unit, gets you on the manufacturer side, does ABS/SRS, and I think the new ones do parking brake, steering angle, oil resets, battery registration, etc. Graphing is poor, but usable for most DIY kinda problems. I haven't used the bigger launch products, but I would imagine their graphing is more akin to my autel 906. The littler stuff usually has mediocre graphing.
Check out what I linked and the CRP129. I think you'd be happier with the 129 simply because you want more detailed info from the car. The little code reader I listed generally has decoded mode $6 for all cars, a HUGE value. Not sure if the 129 has better coverage than mine did when I bought it, most of mode $6 was un-decoded and you needed the tables to figure out what data you were reading. No thanks. The 129 does get you in the manufacturer side, so that chevy should have data lines for each cylinder, current and history misfires counting in real time. Been a while since I used it.
https://www.amazon.com/dp/B07RK9GCK3/?tag=atomicindus08-20
The amazon link has a video on the 129 a guy made, shows the kinda data you'd get. It's a newer GM truck, sounds like a diesel. An older GM will not have that much data, but still more than a code reader will give you on the generic OBDII side of things.
