Why does connection/KBS start high and drop like a stone?

Can someone explain why this happens? You get a connection with a good rate of transfer, and the rate then slower (or rapidly) clicks down to say 0.2kbs if not a flat zero? I ask because I hate it when it happens to me, but more important, I upload like that. i'd say 95% of my uploads are incomplete. They start out good than drop like a stone down to zero, where they never get out of the 0.#kbs range. Unless you have a super fast connection to me, and get the whole file in a flash, your chances are pretty poor. Is there something I can do about this? Or is it my cable provider (Optimum online) keeping my uploads to a trickle? I've read about them putting caps on uploads, but this isn't even close. Any ideas or suggestions?