I have the same problem - no top end power. Merging with highway traffic isnt always fun.
I am hoping that an X-cal 2 tuner will alleviate some of the problem. I think that the intake can be too restricted at WOT. Maybe get a larger throtle body. Make sure you have true WOT. Underdrive pullies will give you more power throughout the rpm range and a full aluminum pulley set will get rid of some rotational mass but that gets pricey.