Which budget factory cam wakes up an early 5.3 — LS3 or LS9 cam?

Jeff Smith's point is that lobe separation angle (LSA) matters as much as duration here.

• What an LS9 cam does on a 5.3: in Richard Holdener's test on a 5.3 truck engine with headers, swapping the stock cam for the LS9 cam gained about 60 hp, to a little over 400 hp. Duration went from 191 to 211 degrees and lift rose by about 0.100 in.
• The catch: factory cams like the LS7 and LS9 use very wide LSAs (above 120 degrees; the truck cam is 115.5) so they idle smoothly. The wider LSA cut overlap, and the engine lost more than 30 lb-ft below 3,500 rpm.
• Why aftermarket truck cams do better: a cam with similar duration on a tighter LSA keeps low- and mid-range torque, and gives the choppier idle many people want.

We don't have a matching LS3 cam test in our sources. For a street 5.3 where low-end torque matters, a truck-specific aftermarket cam is usually the better fit — compare them in the cam finder.