Cornish x rock dieing really need help please

I recently started a poultry farm in Oklahoma, I went threw my first 130 Birds of Astrelopes,Sex links ,Rhode island reds, and Leghorns, With only a 2 bird loss, one i had to cull from the flock at 3 days old due to incubation problems, and one flux accident where a Bird layed his neck over a downed shovel handle and 50 mph wind blew a board over on it.
I ordered 28 jersey Giants, 10 Sex links and 50 Cornish x rocks. I would walk into the cage and find one dead bird a day. I assumed the blood on them was due to cannabalism,
I finally narrowed it down to a black lab who lived up the road. After a 15 bird loss, I got quickly back on track reinforcing the coop to avoid another dog situation.
Being the bright one I am I allowed my australian shepards to herd my chicks with me at night. They are over achieve'r dogs always trying to do the best they can sometimes forgetting to do it with and for me. Again birds started dieing one a day dead in the cage like clock work. so i have ruled out dogs and other animlas now since i rebuilt coop,
I walk outside and see a bird that looked as if it died in the air in my front yard, Quickly i panic and call the state testers who find no trace of bird flu or pull, each day brings a new death until the numbers reach 7 dead birds. I start reallly researching the what could be's ... as i go back outside to check i notice my dog in the chicken coop (the shepard, also keep in mind no birds were bitten or bloody they were just kinda dead like they slept and never woke up.) I walked in and my dog looked so confused as he was trying to herd the chickens into there cages like we do at night time, And at his feet was 4 dead birds who ran out of forward room so to speak. he herded them till they wouldnt move then herded some more.
at least satisfied to know again cause of wierd deaths I chain up the aussie for good while chickens are out. few days pass and here we go again 1 bird a day dead in the cage or in the yard. I know cornish strands are a very hard strand exepecially in flat land Oklahoma where heats can be amazing some days and weather has a mind of its own. there on a sun diet 17-20% protien feed my own recipe corn milo oats Mixed at a local Co Op Wheeler brothers. first 2 weeks are a 28% feed also my own creation. I have a waterer inside and outside the Brooder coop. the tempratures have been 85-100 outside these days. I feed free range birds who go outside at sun up and inside at sunset. these birds are 7 and 4 weeks old they all seem so happy and cheerful and healthy then we wake up to a dead bird, I know it could be heart failure but there diet slows that down I also reduced the protein to assure slow growth (cornish do better this way imo). heres the strange part the 25 Rhode island reds in the brooder next to them are perfectly fine no deaths at all there can anyone perhaps help me with some advice I can provide what ever info you need thank you.

 

Oh i agree I was thinking about going with a slower strand like a red cornish, i had 50 cornish x rocks and now i have like 22 all lost to some unknown cause. Brooders are treated, waterers cleaned and bleached weekly. Windows on all 4 sides of barn chicken wired in. Floors cleaned and disinfected weekly. Boot baths and hand scrubs before and after entering. Poop looks healthy and strong. could it be coccidiosis. One key on my farm i do not medicate any bird on my grounds exept layers for 2 weeks at the start then there switched to a 17-20% protien feed. Leaves me to believe its either heat. or lack of water. I heard in some cases CxR's wont even get up for a drink of water if its to far away from them. also this is my first time with the CxR free range

 

sorry for the bump i really need any advice i can found another dead today temp outside is about 97%f

 

2 to 4 weeks old there is shade everywhere a total of 3 waterers all a fair distance away from the food to prevent lack of exercise. there not dieing 2 or more at a time theres no blood in there stools its been basically one death a day i have had a few breaks where i made it a day but thats it. tempratures are 100% here today H.I. is 109 very humid. There all running around there big pecan tree run happy as butterflys until morning comes then i go out and theres a dead one inside the cage.
I am so mind boggled i have researched this solid now for 4 days i have tried almost every solution that i allow on my farm. I have even had one sent off to the lab state department of agriculture. (sadly it cost to have them tested for anything other then Pull, or A.I.) even read Oklahoma's cooperative Extensions, Broiler Production: Considerations for potential growers. My check list is almost clear minus as i said the few things i dont give or do with my meat birds. almost 200 birds i started, over this operation and only 3 total deaths. how ever none were CxR it has to be me i am missing something. Hope ssomeone else has some background with these things, Because im stumped

 

coyotes howl armadillo's dig in the dirt outside my fence thats buried a foot deep. racoons wish they could but can't. I do see signs of preditors around I remove them from my property as often as i spot them. today they seemed more active the roosters have really grown up fast almost as if over night today was the first time everything seemed to be in order. the bird i found crawled to a bad spot in between a board and the brooder frame. (perhaps the smell of a dead bird to them was killing them via stress) they were all so happy today not gloomy and lifeless we did have a tornadoe over our house and a hail storm with softball sized hail break alot of stuff around the farm in may, Some of the birds were to Hmm. For lack of better words special to get out of the rain they just crammed into the corner.
Perhaps this has some long term effect, I have tried to reason everything i think it could be over and over i got piles of notes but. thre just killing over. I will hope that tomorrow brings a better day. as i said today was the happiest i have ever seen them in a long time.