1996 Vortec 350 issue CODE P0301
From zero to 40 mph runs fine,,,,,From 50mph on it feels like it is missing at speed.....check engine light comes on==P0301.
It shimmys and can make it worse if you manually down shift into 3rd it will vibrate and shimmy and sometimes pops out the exhaust.
Full tune up etc etc etc fuel pump replaced and changed crankshaft sensor. Any ideas?? Truck set up for a year and did not do it before.
Motor has 20k on it. Trans has 195k on it. Maybe convertor?? any thoughts??

Idles fine and will blow the tires off in low if you WOT it. Only happens at cruising speed over 50mph.





