1996 Infiniti I30 P0300 code

Recently had the head gasket replaced and when that was done I bought new champion spark plugs and after it was put back together I am getting the P0300 code. I dont think its a bad plug because out of 6 new plugs the code would mean at least 2 of the plugs are bad.

I sprayed carb cleaner around the gaskets and on all the hoses to see if there was a leak and nothing is leaking from what I can tell.

I did notice that when my gas is around a 1/4 of a tank, the gauge seems to wander around, once it went way down past the E mark. Could this be a sign of the fuel pump going or is there something else I need to check.

I havent had any issues with coils or anything prior to this code coming on. Also I got the code P1402, the EGR valve, but was told that thats being tripped by the P0300 code?

Any Help?