Glad you enjoy the Sonic it's a great product, now I don't want to come off pointing fingers however the fact that the Sonic works with other devices along with the large amount of chatter surrounding the kindle and wifi issues on their forums I would highly reccomend contacting their support:
there is a wifi section that may help or there is a "contact us" on the far right.
Hope it all works out for you, and if you find resolution or need further assistance please post back.
Update. After doing some testing it looks like the extremely slow connection is only when using the browser as well as the App Store.
Once I turned off "Accelerate page loading" under Settings...Advanced in the Kindle Fire browser, the browser started working properly. By default the Kindle Fire has Silk enabled which seems to conflict with the Sonic for some reason. All the other Wifi accesspoints I have used have not shown the same behavior, so I am curious if something is being handled differently.
On a seperate but related note, the Silk experience doesn't seem to be yielding the desired results...http://androidandme.com/2011/11/news/turn-off-accelerated-page-loading-to-speed-up-web-browsing-on-your-kindle-fire/
Thanks for your suggestions!
This is a late reply, but I stumbled across this post noticing the EXACT same issue.
I also have the sonic 4g and just purchased a kindle fire. I noticed the exact same issue. I work with computers, so I naturally have various routers. I noticed this issue was unique to only my sonic 4g.
I'll make it short and simple:
- Everyone knows about disabling "Accelerate Page loading" in Under Web > Settings > Advanced.
-- This fixes the slow browsing issue, but in my case, NOT the slow app store loading/browsing issue that I was also having while using the sonic-4g.
-To fix the slow app store issue, under Web > Settings > Advanced, set Text Encoding to UTF-8. It is on Latin-1 by default.
Obviously, there is some conflict between the kindle's text encoding and the sonic 4g.
I hope this helps someone down the road and will save them several hours of trial and error.