Bank X running rich

Hi all!

2015 Ram, 1500, v6 3.8L, 2wd, Lonestar pkg.

About 4 months ago, had a misfire code at about 100k miles on car, so I changed spark plugs, coil packs, and fuel injectors, and did my best to clean it up in there.

A little over a month ago, I started getting "Bank 1" running rich code. I'd clear it and then later get a "Bank 3" running rich. I keep getting the codes, alternating between different banks (1 and 3 is all I've noticed).

Took it to dealer to diagnose, came back as Engine Coolant Temp Sensor being bad and causing injectors to be rich. I changed out the sensor.

Codes clear for a few days, then the "running rich in Bank (1 or 3)" is back again.

I'm at a loss! If it was consistent, I'd say a bad injector that needs replacing, but with the change... I just don't know what is the next step. Could it be the thermostat valve? I read somewhere that this part goes out and causes temp problems that then cause idling issues.

For the record, the code "running rich in bank X" comes up within a minute of starting up. Once in a while, it will clear itself but then come back.

I'd appreciate any help! The dealership was adamant that only the ECT sensor was the problem, but now I'll have to take it back to them in exchange for my life savings, lol. (P.S. they wanted $550 to change the ECT sensor).