In September 2012, Cranked fine, but sputtered.

In September 2012, Cranked fine, but sputtered and would hardly go. It idled ok, but if rpm’s got above 1000, it sputtered and would hardly move. Code 420. Also had code 1374. This has happened before in May 2011. Ran bad, next morning would run. I had catalytic converter and muffler replaced at this time. In June or July of 2011, it did it again while out of town and local shop in Alabama could not figure it out. It went away and I was able to drive it home. I took it back to convertor shop who said convertor was still good.