I have had the same thing recently. As mentioned by TC, hesitation when accelerating under load can often be misfires through a coilpack in the early stages of being on the way out. The fuelling is another suspect and I wonder if the colder (denser) air can highlight an underlying issue - are you running an uprated fuel pump? Are you remapped? - load control either in the remap or MAP sensor is a less likely candidate.
As TC says, without VCDS logging of misfires, fuel rail pressure, boost and engine load as a start, it is only possible to speculate.