Upgrading help?

[Caleb]

im looking to pull a little more power out of my truck. looking for best bang for buck for my 350 sbc. cam,intake are not options because they are already done. it moves fast for a 4 inch lift and 35's. 0-50 in 6 sec's. after that it loses steam really fast. i mean really fast. so im looking for more top end. turbo, supercharger, heads? looking for budget. i already got a posi 4.11 in the back so thats covered. just what would you guys do and how much money. thanks