Update: luckily it was a pure coincidence. The third plug was extremely loose . Tightened up and good to go.
Did this mod yesterday. Very quick. The downspout does exist at Lowes. Not sure if it matters but part number is with a "-" in front of it. Everything seemed to be good. I do notice the downspout is a bit loose around edges on the stock intake but not enough to be an issue. Drove about 20 miles this morning and was idling in parking lot. Idle dropped to 500RPM and started a varying idle between 750 and 500. Light comes on - Ran to Autozone and it's stating Misfire on 3. I just replaced coils and plugs about 9K miles ago. Shouldn't be bad. I cleaned MAF and pulled battery for about 40 minutes. Went through idle reset procedure as suggested. Still varying idle with shake and sluggish take off. No code (yet).

Could the mod have done this? Seems very odd that I would get this result the day after doing the mod. Any insight or suggestions appreciated. Don't really want to clean/replace O2 sensors but thought maybe that could be it with higher intake.

2007 F150 5.4 Triton - 196K miles. Stock everything else.