You need another opinionfrom another facility.  At the speed
you indicate, the IAC is long since been out of the picture
and, the a/c would be in real trouble if if cause enough
bucking for you to notice it.  I would suspect you have some
sort of ignition malady causing your bucking but, something
as simple as a dirty fuel filter can do that although they
typically cause reduced power more so than bucking.