Slip, VDO. and Check Engine Light On

[And One]

Having a problem with my 2003 G35. The radio goes black and the auto AC kicks in. Now my wife say;s that it feels like it looses power. It stopped this friday but I was able to restart it and it ran fine. Before i spend big money. I would like to try and repair it myself. It stopped the other day and it gave me a P340 code and the slip, VDO, and check engine light were on. I cleared the code but still have the problem. I saw in another post that it may be the cam sensor? Is this hard to replace and how much does it cost? Thanks for any help you may give me with this.

And One