I researched suspension system to speed up the vehicles but my marching times stayed the same?

Not sure on this one. the Suspension system research is to speed up the vehicle troops in the formation. Not the actual APC itself. So if your apc has fighters and shooters in it as well then perhaps it doesn't make a difference. If you have an apc with only vehicles in it (no fighters or shooters) than I would imagine it should improve the marching speed. If you need to check this further probably best to ask the developers using the in game contact option.