Im with the 6.0 guys.
I have gone the 4.8 route before. And with bolt ons and a cam with stock heads, your pretty much limited to about 320-350whp. With FI more, but you can spend $1500 on a cam swap, and everything or you can get a stock lq9 and dyno the same number. Later you cam and stall the lq9 and smile.
The smart thing however would be to put the money twards the note (if you dont own it yet). Its a good feeling knowing that you own a vehicle.