Your Proble is HERE!!!
Every 90 deg turn you pur in a line restricts its flow by 50%. in the simplest terms 4X.75= 3/2= 1.5 1.5/4=.375 so your 3/4" intakes are now 3/8" Solution:> Get rid of those Elbows on 3 of your intakes and use 1 valve. Then do this:
Take that farkn diffuser out start with at least 1/2 chimney of hot stuff and leave the lid off at start up until the thermo hits 200 then put the lid on and let it settle in then put on the meat.