2007 Hyundai Accent (timing?)

Hello! I am in a sticky situation with my 2007 Hyundai Accent. Let me tell you what happened.

The other day I was in Nashville when my car broke down. It seemed to run fine, but when I tried to start it back up it wouldn't start. Without too many details there, it turned out to be a SUPER old timing belt. My brother, who trained in the Navy for automotive, changed the belt for me the next day. All seemed to be fine after he changed it. The car ran great! Much better than it did before it broke down. We also changed all the belts while we did the timing.

The day after we fixed it (~50 miles) I started to have a misfire so I took it to Advanced Auto and had the codes read off.

P0328 Knock sensor 1
P2096 Post Catalyst Fuel Trim Too Lean
P0342 Camshaft Position
P0301 Misfire in Cylinder 1
P0300 Random Misfire
P0302 Misfire in Cylinder 2

My brother thought that maybe it was off time, so we took it back apart and checked the timing. It was fine. I went ahead and replaced the spark plugs (and I did gap them). Didn't help anything.

Anyone have any ideas?