upload and download speed erratic

I don't think this is abnormal. I have an Arcadyan KVD21 5G gateway that always shows 3 bars of signal strength, but download and upload speed can vary greatly. My downloads are anywhere between 35-70 Mbps, with uploads from 5-10/Mbps. I can always do what I want, say, streaming video while running my iPhone and computer, but the actual numbers definitely fluctuate.