I recently fixed my truck that was miss firing in the number two and six cylinder but it is still miss firing at 50 mph. I did only replace the coil packs the spark plugs are still good (I hope) they were changed 30,XXX miles..any thoughts on to what it might be..and also my truck began shifting hard right after the fix, will this be a major concern in the future?

 

30,XXX miles ago forgot to add in truck has 136,XXX MILES ON IT

 

I would try the cheapest, buy two more spark plugs and replace them first.

 

Will do..any thoughts on why its shifting rough all of a sudden?

 

What kind of plugs were installed ??? did you grease the COP's prior to install ?? check your CATS for clog...

 

Did you scan for trouble codes?

 

Motorcraft plugs were installed by the dealership I was scared to do it myself after hearing all the horror stories people had while changing their plugs..and yes I did run a code check but no faults or errors came up

 

no check engine light on?, usually a genuine misfires logs at least a P0300 general misfire code and P030X (x=1-8 cylinder specific) Im curious maybe bad fuel? what made you replace the COP (coil on plug)