What does a spark plug look like on the internal white porcelain at the tip? It should be bone white if it is as lean as you think it is?

Fuel trim? Long Term Fuel Trim (LTFT) and Short Term Fuel Trim (STFT) - these are indications from your PCM that tell you how much your fuel injectors are struggling to keep the mixture close to a stoichimetric 14.7 to 1 ratio. Any of the good Android or IOS OBD 2 code readers can tell you these values. My favorites here using Bluetooth on Android are OBDLink, MotorData OBD, and OBD Fusion. All are very inexpensive or free though to gain access to the extended parameter ID's might cost you 5-10 bucks.

Rick