Temperature Difference in New Construction

I am in Wichita, KS and bought a new house 6/20, and a bonus room/bedroom over the garage was reaching a temperature 8+ degrees higher than the main living space (72-3) or basement (70-2) during August and the beginning of September. The builder does not believe this to be an issue, claiming there will be some temperature difference. I don't disagree that there will be some temperature difference, I don't think more than 4 degrees would be acceptable. They had brought in the hvac installer to check the system twice, and while he had suggested a micro split might make the room more habitable, he felt the system was functioning as designed and suggested keeping the blower fan running 24/7 and keeping the door to the room open. I followed his suggestion and it did not help. The builder said if I wanted a micro split it would have to be on my dime as he doesn't feel responsible.

I am at a loss and am curious if there is any local or national codes surrounding acceptable temperature differences for living spaces? To me with the house being new construction there would be something stating such a difference is unacceptable but I haven't been able to find it.

Any help suggestions would be welcomed and thanks in advance.
Mdwallace

(I describe it as a bedroom/bonus room because the builder says its a bonus room, while his listing agent marketed it as a bedroom and I have the listing, emails between my agent and his, and an appraisal based on his listing showing it as a bedroom, yet another issue I'm sure.)

source https://hvac-talk.com/vbb/showthread.php?2222548-Temperature-Difference-in-New-Construction&goto=newpost