P0301 code came on and the truck is lurching a low RPM on 2004 GMC Sierra 2500 HD

We bought a GMC sierra 2500HD a montha go, low miles. The check engin light has came on a few times and disappeared after a day or so. The we got off of it was P0301. I changed the spark plugs with Irriduim plugs and the code came back on this morning, but I noticed it is lurching when I let off the throttle this time. Any Ideas?

by in Shoshone, ID on March 16, 2012
1 answer 3 comments
ANSWER by on March 16, 2012
POSSIBLE COIL PAK OR WIRE ISSUE WHICH IS COMMON
COMMENT by on March 16, 2012
how does the cylinder numbering go on the new GMC's?
COMMENT by on March 17, 2012
d/s is 1 2 3 4 p/s 5 6 7 8
COMMENT by on March 19, 2012
So I tested the plug wires and coil this weekend. All were functioning fine with the check engine light on. I notice a few other things this weekend, the rpm meter and the speedometer are pretty jerky and the light only seems to come on when I am pushing the engine (ie: when I pass or pulled a hill or haul a load). There have been a lot of modifications done to the intake and exhaust, If they reprogrammed the computer would that cause these issues? Did some reasearchand it seems the was a recall one the instrument cluster but I bought the truck a few months after the deadline.