you would be happier w/ the 4.3, or wait until the 4.2 inline 6 comes out. 270hp out of the box, stock.
My truck before mods was getting 21-22 (w/ 3.08s), now it's getting 19 (w/3.73 limited slip w/ a bunch of bolt ons.. and can't keep my foot out of it).
I have talked w/ a lot of people w/ the 4 banger, rode and drove one myself, and they have no balls. I kinda feel sorry for them. I'm not saying my truck is almighty, but I would never consider an engine that small in our trucks that weigh 3-4,000 lbs.
One of the guys here SuperSlow is getting around 22-23 w/ his ext cab 4. Not impressive if you ask me.