So far the iOS 5.1.1 has fixed the problem totally, and infact it even fixes the weak WiFi issue too.
One thing I did noted, the battery seem like drain faster than before. I don't know whether this is just my illusion, or it is the iOS 5.1.1 packaged with firmwares for wireless chipsets Broadcomm & Qualcomm has re-distributing more voltages or current so both chipsets working ok now. Even if that was the case, I'm pretty fine with that approach which consider better option than no 3G data and I'm gonna live with that till the next iPad (4?) or any other better tablet show up.
f4780y, you're right! I am really enjoying the new iPad since yesterday night 05/08 06:45 pm. I'm gonna marked this date as the victory day for everyone who's has actively participating this problem thread in most iPad forums around the world, including those in the Apple Support Comminuties forum !