TWEST, I agree with what everyone has said. As always, air in - air out. Cold air kit, long tube headers (Texas Speed has/had them on sale), and cat-back exhaust (or no catalytic converters). A tune to take advantage of the air flow and remove some/all torque management. This is a good start.

It is a good idea to add the shift kit and servos to the transmission until you are ready for a full upgrade. Down the road you can look at torque converters and a gear swap if you have 3.42 or numerically smaller.

Once you have maxed out the bolt-ons, you can always look at a motor swap. And actually you could get away with the 6.0 swap without the bolt-ons. Your tranny may not like you very long.

So if you think you are going to want to do a motor swap, then you could always buy the motor and then upgrade it with cam, pushrods, springs, and so on while it is out of the vehicle.

 

This what I recommend......
Custom Tune, CAI, Dual Exaust, Vette Servo, 3000 stall, E-Fans

Than next
Cam, Gears, Shift Kit, NOS, Pulleys