Strange problem with 6L

I have and 04 3500 with a 6.0L

Problem is I have a miss. Two codes keep coming up. P0300, and P0355.
P0300 Engine Misfire Detected
P0355 Ignition Coil 5 Control Circuit

I replaced the spark plugs, plug wires, and also installed a new coil on #5. I still get the same codes. Any ideas as to what to look for. I did notice that the Short and Long term fuel trim was a little rich on back one. Could a bad injector, or intake leak cause this. I'm going to check the coil connector and take a compression test(don't have a leak down tester).

Help, I hate driving with the MIL on. It drives me nuts.

intake leak would normally but not always also throw a lean code. since it is also throwing a p0355, would be a good idea to check the connector and wires going to that coil pack. if those check out good, could be a bad circuit in PCM. i know you replaced the #5 coil, but swap it with another cylinder(#3,5,7 or whatever). if the coil code moves to that cylinder, then you probably got a bad coil....even new it happens. if doesn't move, further examination of wires and such is needed. post back what you find. also, pull #5 spark plug and see if it is kinda black looking...would indicate either too much fuel or not enough spark to burn fuel going in.

I have a little more info. Moved coils around. Same problem. If engine is warm, I get no codes. If I let engine get cold over night, and start it, it can idle for 20 minutes and no code, I start down the driveway and get a code. Once warm, if I clear the code, it doesn't come back till the next day. I'm looking at the wiring harness, any problem areas I should check.

chafing/rubbing, broken and so on. at this point a wiring diagram and multimeter would be useful so you can check voltage and so on. also, what is mileage and how does it run with codes set...any changes or just as smooth, and how did the spark plug look?