Do you use the external GPS antenna? Honestly, I have no idea if/why it would make a difference, but I always do (a Sprint rep once told me, about a year ago, that it worked much better than the internal antenna).
Side note: Again, I'm not saying it's EVDO... I never even gave it any thought other than to note that I always have the Ev icon. All I am saying is the Airave definitely works great for data too, not just voice. 153.8Kbps is more than enough for normal usage. Anything I do that would need more is done on my PC.
