Rough engine with P0300 code
 

Running rough, even more when you put it in drive. Did full tune up. Pulled the plugs today, and #3 and #5 were burnt/black. Thinking either head gasket or spider, any thoughts?

I would do a compression test to see what the compression is all around the motor. I would also pull the plenum and look for evidence of washing from leaking fuel. A fuel pressure and leakdown test is also a very good idea. With all of those tests you should be able to find what the problem is and get pointed toward a fix.

Finally got my hands on a compression tester. i only got one side checked. hoping to do the other side tomorrow. Got about 60 lbs in #3 and #5 cyl, but had over 100 lbs in #1. Im thinking its head gaskets. hopefully the head aint cracked.

still do a fuel pressure and leakdown test.

I already did a fuel pressure check and it holds strong at like 56-58 psi. I don't have a leak down tester. I will ask around to see if I can borrow one though.