First the car would just stumble sometimes and then clear up. Now it seems to misfire drastically on and off after 5000 rpms. Whats wrong with it?

 

My car did the same thing yours is doing a while back. In fact mine just started doing it again lately . Anyway my car was only missing around 5-6 or atleast it was most noticable there. I could also feel the miss if i'd put it in six gear and punch it going up a hill. Anyway mine ended up being a spark plug that was finger lose and the spark plug boot fell off when I took it off. So first i'd check all the spark plugs and make sure they are good and tight. If they are then i'd just replace plugs and wires.

 

I wonder if that explains the code I'm getting for running lean. Or perhaps it is a combination of the cc305 tune with the gm847 cam and tr55 plugs instead of tr5 plugs.