Cheapest is to install a cold air intake and Magnaflow cat back exhaust. Should net at least 15 more hp.
eight hp
keep in mind flowmaster mufflers are chambered. so they wont flow nearly as good as say a magnaflow would. so you will get more HP with a magnaflow than a flowmaster unless you put a flowmaster outlaw series on. its pretty much just a street legal way of straight piping your truck it will flow way good but it will be loud cause there is no ceramic glass packing like magnafow has.
about 5 - 10 hp
Changing carbs probably wouldn't add much if anything, but headers and dual exhaust could give 10 hp.
i just installed a magnaflow hi flow cat 2 weeks ago on my ride i got 4 hp a gain
probably about 30 hp i would know bcuz i own exactley that
Cold air intake, nitrous 75 hp system. exhaust, don't forget to beef your tranny, add a transgo shift kit.
Does increasing the diameter of your exhaust pipe leading from the engine increase exhaust flow and therefore lessen engine burden causing an increase in horsepower? The answer for that is yes, but is negligible. Maybe 3-15 horsepower at best.
145 to 150 hp (single exhaust).
between 10-15 HP
About 3-5 hp