I am another person having a similiar problem! I have a new iPad 64GB + 4G w/ at&t. I am on my 3rd SIM card and 2nd iPad. Within the last 26 hours, I have talked to 4 individuals at at&t and 6 at Apple. Currently I am waiting for at&t to get back to me with the results of a "network check", by NLT 8p on 28 March.......
My problem is that '4G' drops either while I am sitting at my desk or traveling, but does not reconnect on its own. I have to either toggle airplane mode or cellular data on/off. Typically the drop occurs with 2 to 5 bars showing...... Note sure what to do, as both Apple and at&t have told me that there have not been other reportsof this issue.
After 4.5 hours on the phone tonight and 2+ hours with a trip to the Apple store last night, it is getting a little frustrating.
Should note that I am also in St. Louis, Missouri.