Engine overheating and AC cutoff

I have the K series wagon R LXI. Facing issue related to engine over temperature issue. Whenever car going to above eighty mph speed. Engine temperature going up to 115 degrees and that time AC going to cut off. I replaced head gasket and radiator cap. But still same problem is coming. This problem might be related to head? I am confused. Since service station asking for replacement of head, without testing other part.

So, please let me know regarding this issue.