#4 graph has the characteristic appearance of a congested gateway router (redback or BRAS). Parts of #2 and all of #3 might be showing the same, but the packet speed variations seem more diffuse over time and not the with the typically rapid slow down and then rapid speed up pattern that maybe due to a memory buffer filling and then emptying, e.g. like in #4.
#1 graph looks to have TCP/IP layer slowdowns from the server maybe due to overloads on the backbone or possibly due to excess server loads. This isn't a gateway router slowdown problem like in #4.
Loss of sync problems would indicate a DSL layer problem on your line which is separate
from any gateway router problems!
If you can consistently see #4 like graphs in the evening slowdowns, then you should post a trouble thread in AT&T Direct: »AT&T Direct
explaining the evening slowdowns. Only Direct can fix this type of problem by having your circuit switched to a less congested gateway router.
However, If you are still having the sync drop problem, perhaps you should post your modem type and its stats here so that that we can attempt a diagnosis of the cause. Direct can handle two separate problems on your line, but you might be able to speed up the problem resolution if your Direct thread presents both problems from the git go.--