+1 for the code(s). There are no monitors specifically to tell if the injectors are dirty. Yes, clogged fuel injectors could cause a lean condition. But, there might not be an actual failure with the injectors and the DTC could be a failing O2 sensor erroneously reporting Bank 1 being lean. A failing O2 sensor could also cause a lean (or rich) condition.
The DTC for the engine running rich or lean is determined by the O2 sensors. If the problem is isolated to one bank, a quick at-home test for the sensor is to swap it with the one on the other bank and seeing if the code changes to Bank 2 running lean. If your undercarriage is rusted, don't even try this unless you plan to replace the sensors. Other common causes for a lean condition (perceived or actual) are exhaust leak ahead of the sensor and intake manifold leak, although this one usually causes a rich condition.
As for additives, I'm a fan of Berryman B-12. It's about half the price of Seafoam and more potent. I run my tank to around 1/4 tank or less and add a can. I run it until really low then fill up. Unless running E85, I stick to Chevron/Texaco or Exxon. NEVER Shell. I use the B-12 every 3-4 refuelings.