Just finished some work on my Gen 3 Montero, installed new timing belt and kit, new injectors, new ignition coil and spark wires and new serpentine belt. Also did an oil change and admittedly filled it a touch over the mark. After all this, I got into the car, begged the car to work and it immediately jumped to life but then the check engine light came on and this is the code. Says random cylinder misfire. How would I go about diagnosing this?

PS. When I was installing the timing belt, I noticed that the left bank cam-wheel was half a tooth ahead of the mark no matter what I tried to do to make sure all three were in their marks. The previous owner mentioned that he had the valve covers changed so I think that the left bank cover is not OEM and the mark cut out might be off because the crankshaft and right bank cam-wheel are in perfect mark point and the left bank wheel is half a tooth off. Could this be a cause of the misfire?