Repairing my weakness

I appreciate all comments or suggestions so fire away - let me set this up. First of all I am "live" 1/2 NL player in AC, NJ. I always buy in at the max ($300) and my starting strategy is usually loose passive, seeing lots of flops and getting a read on my opponents strategies and betting styles before moving on to a tighter more aggressive approach. The problem I have come across is after I nail someone for their stack and double-up in the first hour. (some problem huh?) No really read on, this always takes the edge off my game. Instead of being aggressive and using the extra chips to push some people around, I always shell-up like a turtle and basically am afraid of giving back the chips I just worked so hard for. I usually just see prime hands (TAG) and wait for monsters to fall in my lap. I usually end up playing for another hour or so then pulling my chips off and go somewhere else and start over. In a way its a great problem to have cause I am winning but I can`t help but feel that I could play better and use those chips to my advantage for even more profitable situations. Anyone else ever get this feeling? If I do it gradually and build my stack throughout the night then it doesn`t affect me, the grind keeps me focused. Its those quick hits that gets my heart pumping and then I get psyched out and freeze up. Any suggestions?

To be honest with you, when I have a similar situation I usually cash out an leave. Most of the times at 1/2 NL it's going to be tough to do much more then double up. Secondly as you stated what usually ends up happening is you dump some of those earnings back on the table waiting for "the next big hand". That being said, getting up and moving to another table is also not a bad idea as long as you're starting over again with the same initial strategy.