I have used Brian at tbichips.com with good success. Another option is the ebl flash.
dont use tbi chips!!!!!!!!!!!!!!!!!!
get a tune when youve done something with the motor or trans, shift kit, cam, heads, intake are all great options and more worthy of a tune than a stock motor.
summit has some nice cheap cams in some interesting flavors, that with some vortec heads and ls6 springs and comp retainers with a nice jegs carbd manifold and youd have a stout motor. as for trans i love the kits that pro built has, dana is the man and hell hook you up. you can either get just a shift kit, a full upgrade kit or the complete upgrade rebuild kit but either way he can tune the seperator plate for whatever your trucks specifics are.
if its a stock high mileage engine then let it blow or wait till your done building a spare block, trust me on that.
im not a fan of edelbrock cams, too expensive or what people usually run in these trucks compared to everything else.