I have a reoccurring problem with a flashing check
You need to know if it IS misfiring. Does it shake at idle?
Typically I recommend experienced techs deal with misfires.
the code should say P030x, with the X being the number of the cylinder it believes is misfiring (No, computers arent always right about which cylinder. USUALLY, but not always.)
Lets assume it says CYLINDER 3. (Only your scanner will tell you for sure, 3 is an example we are using for now). You could try disconnecting cylinder 3 ignition coil plug at idle. On a good cylinder that is NOT misfiring, you will hear and feel the engine run rougher and slow down when you unplug its coil or injector. Thats because it WAS contributing until you unplugged it. Your v6 engine idles at say 600rpm warm when its running good. If you unplug any 1 cylinder, youve lost 1/6 of the engine output (actually more due to dead weight drag from that cylinder, but not important for now). SO, if you find the cylinder it says is misfiring, and it loses rpm when unplugged, its probably doing SOMETHING or trying to. If you unplug it and zero change heard or felt, that cylinder is likely dead.
Heres where it gets hard. Could be literally dozens of things that take some familiarity and experience to ID. bad spark, bad fuel mix, bad spark plug, oil fouling, low compression, leaky valves, blown headgasket, leaking intake, EGR leaking at idle, wrong weight of motor oil (some cars) and the list goes on. An experienced drivability tech can usually narrow it down or find it in 1 hour or less. If you are learning as you go, you could take many hours, and still miss things that trained eyes and ears wont.
Start by figuring out which cylinder. If it idles smooth (No shake at idle, and if you clear code and start it and let it idle the light never comes back till you drive over 75 as you stated), then I strongly recommend a professional check it.
If it idles rough and you know which cylinder, you can try taking out that coil and spark plug if you know how, moving them to another cylinder that isnt misfiring, then clear the code and drive it and see if the same code resets or a new code for the other cylinder sets. If the code is the same, you have deeper issues not worth explaining here.
If the code moves to the new cylinder, then 1 or both of the 2 parts you changed are likely at fault. You can replace them an very likely fix the issue.
Again, I strongly recommend professional help. But that may get you started.
on Jan 04, 2018