I agree with you about the diagnosis, but..
Make sure to try factory resetting as well (little button on the back, use a paperclip or something to get at it). You aren't supposed to run into congested channels with an 8 channel modem, but it is worth a try. Might improve some other settings as well.
Definitely do it in the evening when the problems are occurring so that you can have a clear idea if it helped or not. It can take half an hour to come back online, so be ready for a bit of interruption.--