3.5 will not rev over 3500 rpm. PO 449 is the only code stored. It will not rev over 3500 cold or hot. After driving 10-15 minutes seems like the transmission is searching for a gear, just what it acts like. Then top speed is on 10 mph for a bit then picks back up but still will not rev over 3500 rpm still bucking. I do know that it's not the catalytic converter. Any more ideas.