Lately the day time is from 90-100. Night time is from 75-80. They go out on the cooler side of the day and have half shade and half sun so they have a choice. If the temps are good with low wind I will let them outside several times a day. At night they are inside as I have no way to control the outside temp then. It was 96 when the ill ones wanted to stand as close to the heat lamp as possible. I thought that was strange. When the temps get a little warm I look for signs of laying in the shade and their breathing to see if they need to come inside. Right now they have an 8'X8' (non stop it seems it needs to be moved) run and within the next couple of days they will be moving to the big run. When they come out of the brooder I plan to let them free range with my flock.
With temps like that, I don't know that I'd be using a heat lamp at all...maybe you could try it a little and just observe their behavior. Was thinking maybe the hot temps of the heat lamp coupled with the heat from the lamp might have contributed...or not...just spit ballin' here.
It is strange that they wanted to stay close to a heat lamp in those kind of ambient temps...my meat chickens would have died outright if I had provided heat with ambient temps at 75...I took away their heat lamp at temps of 50-60 and let them provide their own heat for each other.
But, yours are just a few days old, aren't they? Could be they still need a little warmth?