I don't know if this has been addressed before in regards to the dropping 4G problem (I see your problem has been fixed brennan77), but I was experimenting with trying to get even more battery life the other day and decided to turn off "Always on data connection" or whatever it's called. I then noticed over the next couple of days that I would lose my 4G, 3G, and 1X connection and get nothing, even when I tried to turn the connection on/off, tried to use internet, or toggled the "Always on" setting. I had to restart the phone to get my connection back. So, I just toggled it back to "Always on" and it has worked fine since. Perhaps some have experienced the same issue.
Interesting. I never did toggle the always on feature. I will say that the replacement phone has been a completely different experience. I've not lost data once. And with my extended battery, I have seen nearly 16 hours today without being plugged in. My battery is still at over 72%. I've played games, searched the net, played on facebook, read my newsgroups, downloaded from the market, etc.
It's been a great phone over the last couple of days with the exception of some oddities with car mode and my car charger.