iOS 4 on iPhone 3GS reception signal problem?

Ever since I updated to iOS 4 on my 3GS, I can say I have only 4 bars of signal or even lesser. Only 2% of the time I see Full Signal

The point is, the iPhone 3GS never used to do this until the iOS4 update. This very well could be a software issue.

Remember iOS 4? iPhone 4 with iOS 4 had antenna problems. So, Apple released  iOS 4.01 which Apple claims to fix antenna problem. Maybe on iPhone 4 but not iPhone 3G and 3GS

Apple officially accepted that all versions of iPhone 4, iPhone 3GS, and iPhone 3G were displaying wrong signal strengths.

Upon investigation, we were stunned to find that the formula we use to calculate how many bars of signal strength to display is totally wrong. Our formula, in many instances, mistakenly displays 2 more bars than it should for a given signal strength. For example, we sometimes display 4 bars when we should be displaying as few as 2 bars. Users observing a drop of several bars when they grip their iPhone in a certain way are most likely in an area with very weak signal strength, but they don’t know it because we are erroneously displaying 4 or 5 bars. Their big drop in bars is because their high bars were never real in the first place.
To fix this, we are adopting AT&T’s recently recommended formula for calculating how many bars to display for a given signal strength. The real signal strength remains the same, but the iPhone’s bars will report it far more accurately, providing users a much better indication of the reception they will get in a given area. We are also making bars 1, 2 and 3 a bit taller so they will be easier to see.

You must understand that the reception would not change, but merely the signal bars would be more accurately displaying the signal. Steve Jobs has announced free Bumper cases to improve reception for iPhone 4 users.

iOS 4 works with iPhone 4, iPhone 3GS, and iPhone 3G, but not all features are compatible with all devices. For example, multitasking is available only with iPhone 4 and iPhone 3GS.

So far, I have no drop call at all. Definitely is the software issue. Wrong calculate? Or all the while Apple's signal is bad.

I was thinking going back to 3.1.3 but I noticed some improvement such as faster photo taking on iOS 4(Click as much as you like, It's like multi-shot) and e.g

Well, we'll see then