That sounds like almost certainly a wireless networking issue. The rather mediocre help offered by netflix is unfortunately about as much help as it is possible for them to offer. Diagnosing a slow network over the phone is nearly impossible.
Streaming full length programming over wifi is not terribly reliable. What you're describing are exactly the same symptoms as have been experienced by millions of other people who attempt to stream video over wifi. The type of device in use (an AppleTV) is mostly entirely irrelevant.
To find out for sure if it is a wifi problem, it would be best to temporarily connect the appleTV via a wired connection. Granted this can be difficult given the layout of some homes and where the router is located.
While using a wired ethernet connection is the ultimate solution, changing wifi channels might help as well. This is same type of trial and error solution as switching to 5Ghz.
If neighbors have recently turned on a wifi router, or installed new appliances, it is possible that there is now interference when there wasn't in the past. If not wanting to get into more complicated testing and diagnosing, it might be worth trying a different channel. If neighbors are using the same channel, this could fix the problem. Note though, that wifi channels overlap eachother. For example, channel 1 overlaps with 2,3,4, and 5. Channel 6 overlaps with 2,3,4,5,7,8,9,1. etc. It is best to choose a channel number as far away from everything else as possible. (Graph of overlapping channels: http://4.bp.blogspot.com/_pzC_7PLtN-...Channels+1.gif