I posted this answer for you over on bowtie.
I know how you feel. Depending on the dyno, the time of day, weather and a few other star alignment factors getting dyno numbers is tricky. Try not to use it for total new HP over what you had.
Did you dyno bone stock at the same place?
Was the conditions exactly the same when you did both dyno runs, (stock vs. mods)?
Did you go back to the same dyno shop for the mod runs?
HEre is a link to a GREAT article that I have posted many times for people to get an understanding about dynos. Read the article and you will get a good feeling about how dynos are ALL different.
http://www.hotrod.com/techarticles/gene ... o_testing/
Also, I have similar mods, OBX Headers, INJEN CAI, Ported Throttle Body, Black-Iceolator, MRT Axle Back, Magnaflow resonated X pipe, and Trifecta Tune. I did my first set and only set of dyno pulls for a charity event. I was not overly excited about my HP #'s either. 261 However it was a warm, humid day on a portable trailer dyno. I was impressed with the torque numbers thou. 263 with it over 250 from 2500 rpm's to 5000 rpms
I just did a new 0 - 60 run this morning, first time in a long time. Ran my best to date. 5.23 comparred to a previous best of 5.5.
I have made over 100 passes at the track and have them all on a spreadsheet. As a whole adding all my stuff together shows I have made good gains at the track.
Hope this helps a little.
Mike
PS: I have $2400 into all of my investment, including tax, set-up frieght, shipping, handling, welding, dinner for an installer, etc.