Looks good for your first HnF go around brotha, I usually stick with 10-14# briskets they seem to yield a tenderer brisket then the big 17-20# ders. The 10-14#ders after trimming you lose about 2#ds so they cook even quicker, I did do a 17# CAB Prime awhile back and it took 8h at 300-350* and was tender but I also thought it was kinda dry kinda like what your saying. I'd rather cook two 10# briskets then one big brisket but I'm sure others feel the same. Try a smaller one like a 12# the same way and see if you get what your looking for, happy smoking brotha
Also I check for softness and flexibility still when I pick out a brisket.
Edit: I didn't even think about that foil pan rack system you were using, I'd say ol' dawg is on to something here
That's what your issue is you need to do away with the foil pan/rack and go straight on the grill grate, try that on you next smoke and see what happens.