5.3 chevy Horsepower increase
Cold Air Intake, cat back exhaust and a tune will give maybe 20 HP. Anything much higher than that would require camshaft, cylinder heads, intake manifold and headers. Best thing might be to swap in an LS2 or LS3 engine. Horse power these days is not cheap.
Dusl exhaust, vring in as much fresh air as you can...
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