Was there any thick white smoke coming from the exhaust? If not then I doubt its a headgasket. More than likely its the LIM gasket.
How fast does it eat coolant?
Also, what was empty on coolant, the resivoir or the entire radiator?
Misfire could be a bad wire or coil. May also come down to a compression test on that cylinder. Try switching wires w/ another cylinder and see if the misfire follows that wire or stays on #3.
On the P0716 code try this...
Hey guys. I just wanted to give an update on this. I took a look at the wires between the transmission 20 pin connector and the PCM and I noticed my CAI wore through some of wires connecting to the PCM. Turns out the ISS wire was shorting out on the metal fibers on my intake. I wrapped the damaged wires individually with electrical tape. My torque converter is locking up properly again, and my car has no issues shifting to 4th gear! If you have a P0716 or P0717 code, check those wires!
