modem troubles

so my parents decided to move the main computer and we needed to move the modem along with it, and to compensate my dad gave me a modem he just had “lying around” that he “found”.

They’re both Motorola SBV5120’s provided by cablevision, and we hooked them up just right. now, the problem is, that the modem i have has a max internet speed of like, 30 kilobytes per second, at best. now the other one can go to about 1.5 megs/second downloads, and it works fine when i replace mine with it, but my father needs his modem because the phone only works on his as well.

is there anything i can do to fix this damn internet connection? i’m on it right now, but it’s just so slow. it’s not a location problem, because his works the way it’s supposed to here where i’ve got it.

much appreciated