The internal .data will store the raw dataset in uint8 with values in the range [0, 255].
The mean of these values (transformed to FloatTensors) would thus be 33.3184.
Normalizing the raw data with these values would thus work.
However, since ToTensor() already normalizes the tensors to the range [0, 1], the mean and std in transforms.Normalize should also be in this range (divided by 255.).