iDirect 3000 connectivity

Hello
i had small problem two month ago i had problem with pointing my dish to 68.5 Deg E but i manage to solve it but few days later  i began to lose connectivity so i had to do it again but i had to do it properly because i do it last time in rush and my service provider told me to get between 16-17 V and iam able to get 16v .and every thing seem fine . but when i connect my network to internet i found that the internet is very slow so i make several speed test and  the result was very strange some time i got about 200kbps and some times get only 90kbps. so i know definety there some thing wrong so i fire up my isite and found that my Downstream SNR is varies from -10.5 to -11.8 dB and tx power is about -16dBm . and i think i read some where that two variable  had close relationship with the internet connectivity so ineed some help on this since iam completly new to this.