Have you determined what the cause of these problems are?
I live in an outlying area, so my coverage varies which can have an effect on how well the phone works. But still I don't have your problems. I use my phone for all my digital data: both on the phone and as a digital host, so it is running all the time.
I could make a couple of guesses based on my experience of a phone user and also a few years developing test solutions for phones.
For problems like powering down:
The first would be that you second phone is also defective; the manufacture has very little time to test the phone, they test the transmitter and receivers and then any other test is some sort of quick and dirty self test. From the complaints I have read I would not be surprised that there are lots of defects that just keep getting passed through to the next customer (just my guess here, but this would be a consistent issue with all phones, the users become the real tester).
For problems like:
No or late email, email load errors, those sound like network connection lost errors. The late email can be checked by you: there is a setting for how often the phone looks for email and also you can launch the email app and have it check that way. I have observed that sometimes my local digital network is unavailable to me even when I have good signal. Why this happens I do not know, but I can be working away on my laptop and all of a sudden the data rate goes to zero, and I check the phone and the network power looks good on the phone's power meter, but there is no digital data connection. In a short time, say ten minutes the connection is going again. This is not a network problem, it is a problem with the combination of my phone, the network, weather conditions, and even time of day.
I too have used my phone while driving a car. But I can hear folks just fine, it is true I put the phone in speaker mode, that seems to make the difference.
As to battery lasting:
Gingerbread has helped here. I have used an application to improve the battery life before GB, it helped a lot. But my recommendation is that if you are using the REV as a phone then the battery is fine, anything else (navigation, browser, Bluetooth or any other use other than phone) and it needs to be on a charger. Sure you can look up a couple of things on the Internet without a charger but prolonged use and the battery will go down quickly.
Hope this helps, it is a hassle changing networks. I would recommend that you test out these phone issues before you make the switch.