An electrical connector assembly comprising: an insulative housing with a front mating slot and a rear receiving cavity; a combo contact module assembly received within the receiving cavity and including a sideband contact module sandwiched between a pair of high speed contact modules; each high speed contact module including an upper unit and a lower unit assembled with each other in a vertical direction; the upper unit and the lower unit being essentially symmetrically arranged with each other in the vertical direction with a half of pitch offset in a transverse direction; and a metallic shell; wherein each of the upper unit and the lower unit including a front subunit and a rear subunit stacked with each other in the vertical direction and retained together.