2006 V6 will not rev past 5000
 

A few weeks ago my CEL turned on, I had a look at it and it threw out P0300, ended up changing spark plugs and wires, witch seemed to make it go away, and ran fine for a week or two.

The problem now it that when I floor it, the revs start climbing and once they get to about 4500 it starts to slow down and will not go any further than 5000,
and if i keep the revs held there for a few second in 3rd gear the check engine light will start to flash but once I get it back down towards 40mph it will turn off completely.
I've read around on threads for similar issues but haven't found anything just like this. Does anyone know what my problem could be or where I should start looking?

do you have any new codes? I am assuming it is in limp mode

Limp mode? At 5000 rpm? My understanding of limp mode is the code expressing "Forced Limited Power", which means just that......depress the gas pedal, little response, transmission shifts jerky, unpredictable......

Sounds to me like you are hitting the rev limiter.

was there any new codes, perhaps post a video of it doing it?