technicall question about d3 cable modems speed issues

[rapidfire]

hello i cant understand some problems in my isp networks
lets say i have legall d3 cable modem cisco epc3010 with 120mb speed
in reality i got just 30mb in night and in day 15 - 20mb
when i take that modem and going to my friend far away from me i got on his cable line speed up to 60mb
this cable modem in my house bond just to 1 channel download and 1 upload 1x1
with d1 cable network in my house everything is fine no glitches tested with uncapped modems running even up to 50mb cause i have eurodocsis and speed is allways same
my question is why this is happens ? is there are some isp limitations with d3 network in some areas ?
even if yes then for sure d1 network is 80% much overloaded with old clients than d3 which is almost new
the signal levels i have as follows
downstream channel 1 -8.5 dbmv , signal to noise ratio 37.6dB
upstream channel 1 power level 57.0 dBmV
the rest of channels are totally off
i did read in some websites and people around confirming they had similiar problems they pay for 120mb and got only 60mb some of them got like they should 120mb , calling and stumbling isp doesnt change basically nothing they send the techinician into yours house he check something and smile and goes away
thanks for any hints

[rapidfire]

anybody can help ?
thanks

[bayb00tl3gg3r]

there are many variables that affect the speed you get. The advertised 120mb is often the burst speed, the maximum your connection is capable but not necessarily will achieve on average. You also have to consider the physical layer of your connection, how good is the connection? how saturated is it? etc.