sometimes I get 0 kbps or 4-5 kbps download speed and some times 200-300 kbps,inconsistent download speed it keeps changing
I found tata docomo economical and consistently good (speed), during tech issue it was bad like what u r facing.
if issue is from your end then
Check for good antivirus, uninstall unnecesary applications, use msconfig to check/ start -stop some unwanted services,applications. Disable firewall-antivirus for testing purpose!
customize your windows to run on performance based instead of good visuals.
Now check the performance of system and net.
one more thing i personally experienced, that post paid 3g dongle work consistenly good with speed and without disconnections. Cant claim is 100% true but i was facing issue of internet disconnection after few hours but that has issue has resolved with the pospaid connection of same company 3g sim on same old cracked/hacked data card.
try vodafone as well or airtel 4g.
Hope that helps