Check engine light on, check engine light flashes intermittently, codes 300 and 152

Hello, so you did have the coils and spark plugs changed out. The P0300 random misfire code can be caused by ignition coils and spark plugs. But the other code, it's 152, i assume you mean p0152? Thats a Bank 2 Sensor 1 Oxygen sensor code voltage High. Meaning that oxygen sensor is reporting a very rich condition on that bank, or side of the engine since this is a V6. This can be a faulty sensor. If the sensor is stuck at a high voltage signal, it is telling the engine computer that Bank 2 side of the engine is very rich, and the engine computer will compensate for that by reducing the amount of fuel on that side of the engine and it will definitely give you cylinder misfires because of the lack of fuel.
So, your mechanic needs to monitor that front oxygen sensor on Bank 2 and make sure it's active.
The oxygen sensor also has a heater in it. If the heater is not working correctly the sensor will not be active at all. But if the sensor is just sitting at some high voltage, the code criteria is voltage above 3.99-volts for more than 40 seconds, then the sensor is most likely needing to be replaced. I think you'll find both codes are related.

https://www.2carpros.com/articles/how-an-oxygen-sensor-works

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

You can try that. But if you have a code reader that can give you a live data stream, some of the cheaper scan tools can do that too, I would observe the right front oxygen sensors activity. Also inspect its wiring the dark blue/light green wire is the signal wire going to the ECN. The brown/violet is the heater circuit 12v feed. Swapping the sensor can be tough, getting these sensors out sometimes takes the threads out of the exhaust with them. I usually get the engine and exhaust hot first, plus you'll need an oxygen sensor socket. The right front will be the passenger side oxygen sensor before the catalytic converter.

So, most likely your scan tool is going to give you generic OBD2 data. Since it's not a high-end scan tool. So, the oxygen sensor voltage signal will be either 0-5-volts or 0.200-0.800mv range. Below is an example of an oxygen sensor signal, in red, the first half is the correct operation. The second half in red is a lazy or slow responding oxygen sensor. So, you will most likely see a stuck high voltage signal, if you do, create a vacuum leak and see if the sensor responds. Take off the brake booster hose that goes to the intake manifold and allows it to pull air in, the sensor should go lean, meaning low voltage, if it doesn't then most likely the sensor has failed. Just a quick test you can do to see if it will do anything. Since this code indicates a pretty high voltage signal, and you see it reading something like 5 volts, then the signal wire might be shorted to another wire and that's where the voltage is coming from. In that case, if you have a multimeter, turn the engine off, but Key in "on" position, unplug the sensor and check the signal wire on the harness side. It should not be reading high voltage at that point. If it still is the same reading, then it's not the sensor. It's probably a wiring harness issue. Just don't stuff the multimeter lead into the oxygen sensor plug, just touch the connector pin lightly. Ground the other lead of the meter to battery negative.

Okay. So, it goes 02 Sensor 1 Bank 1 and 02 Sensor, Sensor 2 Bank 1 (rear on that bank).
The 02 Sensor 1 Bank 2 is the front oxygen sensor for bank 2, that's the one that the code is for, it should be fluctuating between 0.200-0.800mv, so that sensor is stuck at 0.860mv, that's the issue here. If you took off the brake booster hose and that number didn't move at all. I'd say that sensor is not good. And no, don't ground anything. The rear sensors should hover around a fixed voltage level. The only other test you can do is to check the heater circuit, but you would have a code if there was an issue with that circuit. So, you need to replace that right front oxygen sensor (passenger side). Clear any codes and take it for a good ride. See if any codes come back. They shouldn't. The bad oxygen sensor is leaning out that bank and the lack of fuel is causing misfire codes.

And also, you wrote that Sensor 2 Bank 1 was fluctuating? That sensor shouldn't be changing. Is it possible that the wrong sensor is hooked up in the wrong place? I have seen that before. I'm going to put up the wiring colors for each sensor so you can check that.

I was curious, did your mechanic check the front oxygen sensor with that code?
Below are all 4 oxygen sensors, the rear ones will be behind the catalytic converter. The Right side is the passenger side. Make sure someone didn't plug the driver side front sensor into the rear sensors wiring harness.

Yeah, the oxygen sensors may even be the same part number, but for example the bank 1 sensor 1 harness plug needs to be plugged into the sensor that's in the Bank 1 sensor 1 location. Thats what I was meaning. I have seen a Bank 1 Sensor 1 harness plugged into the bank 1 sensor 2 location. And that will skew the ECM's data.