preferred plan. slow internet evening

I had a docsis 2.0 modem which was experiencing slow internet at night starting the past few weeks. Upgraded to a sb6141 on Fri. Top speeds met advertised speed of about 60mbs around 6pm on Fri. Fri night speed dropped to about 10mb/s. Daytime speeds on sat were around 30mb/s. Sat night speed dropped to 1mb/s around 11pm-1am. However upload speeds were much quicker. Around 11mb/s or more. 

Not sure if firmware issue of modem. Or Internet problem of area. I've tried the tests with router removed and PC connected directly to modem. Please advise.