I bought the ANCEL AD310 code reader via Amazon a few months ago. It works well, and does give some live data feeds for diagnostic work. It’s not a fancy model but for $35 I’m happy.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
I’m not sure about your oil change questions, but I would imagine the oil weight and type to be responsible for the pressure change and not the filter bypass spring (I think that would be set much higher than 40-50psi to bypass excessive pressure). For reference, my 04 Burb’s 5.3 has nearly the same pressure readings with 281k, a regular WIX filter, and 5-30 conventional oil.