Clifford Faught

Working on a friends Lancer. Its an automatic (ewww) with the 2.0l. It recently started running rough with an accel issue on the low end. From a stand still if you try to floor it, it accels real slow and the end will dump the RPMs. But it seems to surge a little bit and once you get to higher speeds its not as noticeable. I did a scan and there are 2 codes. P0301 for cyl 1 misfire and P0421 for the Cat. I changed all the plugs to NGKs. I have my own lancer (its standard and running fine) so Ive been swapping over parts that are the same in the hopes that I could more easily pinpoint the issue. But Ive been able to find nothing. Ive googled this problem and everything I find is just more questions and with either no answers or vague suggestions that the OP never comes back to confirm if it worked. Im hoping that someone on this forum has had this exact issue and knows the definitive answer.