You may be seeing the same thing I experienced when I tried to upgrade a while back. I'll have to do some digging to find the topic.
What ended up happened in my case... I reverted back to my old package. Although the new package was faster on the top end it had such a slow ramp up after the upgrade that I favored my old package.
The new package required a new modem (16 channel). As with many previous cable internet speed upgrades over the years I was excited to upgrade, newer modem usually means great things. But that's just not at all what I observed with TestMy.net. Other tests, especially speedtest.net, will show higher results. They don't work like TestMy.net... they combine threads to achieve the highest possible speed. Good to know but it only shows part of the performance picture. For a multithread comparison within TMN you should try TestMy.net's multithread speed test - make sure you disable the option when you're done to test as you normally do.
My conclusion was that the newest, "fastest" packages from Comcast we're not what I was expecting. Again, fast top end but really slow starting out. It's like having a Lamborghini that can only drive in 4th-6th gear... eventually it will win a LONG race but for most stuff it just didn't stack up to the slower package with less threads. The "slower" package jumps off the line like a Tesla. Instantly up to speed with little ramp up at all. By the time the 16 channel modem would ramp up my "slower" modem/package was already done with the race ...and the next one.
Sometimes higher package speed doesn't equate to higher results on a single computer. It might just equate to more computers and devices that can be aggressively pulling resources without affecting each others speed as much. Personally, I favor my off the line performance more than the top end or being able to serve more devices. Especially with how bad it was in this case. I switched back and my results instantly fell back into line with the performance curve I expect. By the way, I'm still easily able to serve over 20 devices on my connection.
That was the first time a cable upgrade disappointed me and needed to be switched back to previous settings. Hey... at least I saved money because I no longer needed a new modem and the "slower" package is cheaper. TestMy.net saved me money by showing me that I actually performed better on a cheaper package.