Different fuel trims per engine bank?

[ENT-Z]

Hi Guys -- I got a CEL and it was the random cylinder misfire code, not specific to a single cylinder. It has actually gone on and off a few times over the last several weeks. My car has TPs, post MAF tubes/K&N filters, FI exhaust and a Uprev tune. I haven't driven it hard in several months.

Only real noticeable difference driving is that when the CEL is on the idle is about 300 rpms faster (1000 rpms) then when it is off. Interestingly, when I switched out of the performance tune to the factory tune, the car did studder and seemed to have fuel starvation at around 3000 rpms. I quickly changed it back to performance tune and it drives fine.

Mechanic found that the fuel trims were very different per engine bank. One side is like +18% and the other side is only a few %. He cleaned the filters and the MAFs, checked for vacuum leaks and it still was the same. So he swapped O2 sensors from one bank to the other, thinking it may just be a bad sensor. The fuel trim difference did not change, indicating the O2 sensors are fine. So, we are thinking maybe fuel injectors? Anything else you guys have seen before or can think of?

Thanks!