I also have an 03 and it was stock until J. Cleary let me load a few Smarty programs. Well it only took about 1 minute before I fell in love with it and didnt want to give it back.
I think the Smarty is hands down the best downloader and you cant beat a Smarty, mp8, tst stack on a 03-04.
My truck is pretty much stock except Smarty, MP8, Silverbullet, stock clutch and fuel system. The clutch was slipping with the Smarty alone and since ive added the silverbullet and mp8 it slips really bad but theres still a way to baby the clutch.
Well I just got back from a dyno and was still able to get respectable numbers for having to wait until 2,000rpm until I go WOT and only 40% on MP8, and Smarty #9. My best was 433hp and 831 tq.
The truck feels really strong with the mp8 75%+ but the clutch wont hold it under dyno load but it flyes on the road. I dynoed 418 hp and 820 tq a few months ago with a EZ instead of mp8, but ill tell you the mp8 feels twice as strong as the ez.
Im hoping for 500 once I get a stronger clutch and a walbro. .
and 570hp with a TST...