I am just seeing this, I would not have set up the fire like you did. Bludawgs tip about the grate is 100% on, that is really important. But...
In a kettle, top vent wide open, bottom vent no more than 1/8" at widest part, that will put you close to 300F. I use three to four small pieces of wood, not two large pieces, as the burning wood ignites far too often, the smaller pieces will also, but, will not affect temperature. A kettle has too small of an air volume to take larger pieces of wood. I pile up briquettes as you did, but, I use 5 or 6 lit briquettes, place them on the pile and let it run up to temperature first. At 225F, I put the meat on, then leave the vents at no more than 1/8", this works fine. The kettle will climb to 300F over an hour. Then it will settle around 300F to 325F. At these temperatures, I do not foil, I either pan or butcher paper, if I do anything at all.
With a pan, I use a aluminum or steel pan, preheated in my oven, add 2 cups liquid, maybe 3 cups, to get 1/2 inch of liquid, then a rack, to keep meat above liquid, then meat and finally cover with foil, does not need to be airtight.
With paper, I use a double wrap of butcher paper (uncoated is key) spray with a little liquid, then gift wrap and into cooker. Again, does not need to be airtight.
Either way, cook until probe slides in easily, then rest for at least 2 hours. I believe you were too hot and with foiling, you just overcooked it a bit/lot.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"perhaps...but then again...maybe not..."