Need advice: Keep or Replace Docsis 3.0 modem

So In the past two weeks, I heard about Cox raising speeds for the Pref and Prem tiers,

and thought this would be the time to replace my 10 yr old Docsis 2.0 modem

with a Docsis 3.0 modem.

Since in the past Motorola has been good to me, I went and purchased a Moto 6121 that was on sale at

Amazon for $68.

Since installing the modem, I've had a roller coaster ride: THe Modem got installed two Sundays ago, and it stayed up for

about a day, and then I saw Speeds of 120Mbps up / 0.1 down. I called Cox, they re-provisioned the modem, and

things got stable ( 76U/12D) and I was able to enjoy internet. Tuesday, it did the same thing again 120U/ 0.1 D,

and dropped off completely ( Cox couldn't even see it online, even though it had power and was lit up).

I had to do a manual reset, and it stayed up for 30 mins before dropping again.

Cox Tech came out later that day, said it was a "signal problem" first and foremost, and found to be

the cause of that a squirrel had ate into the line coming from Pole to House.

He replaced that line, and upgraded my box ( I had a booster on the line since 2001)

which he said I no longer needed.

Came back in the house, tested, I was getting 80U/20D at that point.

I asked him about the modem, and he said that they were having issues with the

Motorola 6121's, and weren't recommending them anymore. He said in fact, that

if I upgraded to the next tier, my moto 6121 would not even work well on it.

His recommendation was to instead get a Netgear or Cisco modem, like the DC3010.

so all was right for the next four days then on Saturday, same thing happened

again....got 120U/and 3D this time, and Modem went offline.

I called Cox, and was able to get it back on, but now I'm worried about it continually happening.

Amazon had a Warehouse deal on the Cisco DC3010 for $47, I'm tempted to buy it

and send the Moto 6121 back as defective....but I got to thinking...could this have something

to do with the updates Cox pushes out during this time of "boosting " the Prem and Pref speeds?

and if so, how do I know I won't have the same issues with the Cisco DC3010?

Anyone's thoughts are appreciated esp. moto 6121 owners and Cisco DC3010 owners

during this "upgrade speeds" phase...have you been having any issues like I've had?