NEED HELP DIAGNOSING, perhaps coil pack but non-traditional symptoms

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Oct 30, 2014
Boston, MA
Cliff notes: Highway speeds, downshift for hill to higher RPM and lower gear w/ moderate throttle and there's a rapid development of shuddering and then flashing CEL w/ VSC and other light on. Throttle lifted, lights gone and running great. Engine never seems to miss a beat.

Driving along today, the truck downshifted for a hill on the highway and holding at higher (3K plus) rpms and after about 2 seconds at this RPM with moderate throttle, a shuddering developed somewhere in the driveline and if I held the throttle there, I got a flashing CEL for no more than 5 seconds with the VSC and other (didn't get a good look) light on. I backed off the throttle in panic and everything disappeared as if nothing had happened!

The engine never ran rough but then again I did back off to be safe. It seems to occur when the tranny is trying to shift perhaps? I recreated the scenario again after thinking about it and was able to do it again, and same thing happened. I drove it all the way home 2 hrs with no problems, no hesitation or rough idle.

I'm really stumped guys and could definitely use some help. I read through the coil pack FAQ but I'm not getting a rough idle or hesitation etc so I'm a little stumped. Thanks guys!

Sounds like the beginning of a coil pack failure. If you have an autozone nearby you can see if any codes were stored?
My initial thought was coil pack too but wouldn't I have a rough idle and hesitation during normal driving as well? I guess since this was such a unique circumstance and it ran smoothly the whole way back I figured it was something else, but perhaps you are right.

I will go to Autozone tomorrow to see what I can find out, but I thought that since the light went out so quickly that nothing would be on there, but I'm probably wrong about that as well.

Thanks RND1, any other suggestions are welcome.
Pulled code, confirmed it's a bad coil pack, p0301. Surprised by this considering the truck is running like a champ aside from the above situation. Ordering new ones from Beno now, keeping an Autozone one in the truck in the mean time just in case, still need to get to VT this weekend for some skiing :)

As always, this place has proved to be a lifesaver, thanks guys!
Glad it was something simple! An Actron pocket scanner is only $40 from Amazon and all the codes are in the MUD FAQs. I carry a cheap scanner in the tool bag in each car now.

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