Does a lowered truck need a different oil pan, or will the stock truck LS pan work?

Usually a different pan. Speedway measured the stock truck pan at more than 8 in deep, about 8-1/2 in on their 5.3, hanging 2–3 in below the crossmember in their swap. An F-body-style pan is about 5-5/8 in at the sump, more than 2 in shorter, and in most cases sits up where the crossmember protects it.

Junkyard LS pans often hang too low (sump depth) for muscle cars/hot rods; low-profile swap pans fit most chassis; baffled/ventilated pans help oil control in hard cornering.

Pan	Sump depth
Stock GM truck pan (Speedway)	over 8 in (about 8-1/2 in)
Chevrolet Performance Muscle Car swap pan	7.75 in
GTO / VZ Commodore (front sump)	6.3 in
Moroso LS swap pans	6 in
Holley 302-1 retro-fit	5.99 in
F-body Camaro/Firebird	5.62 in (Speedway: about 5-5/8 in)
C6 Corvette wet sump	4.85 in

Pickup O-ring: lubricate it generously with oil when installing the pickup. Speedway warns a dry O-ring tends to tear and cause oil pressure problems. Measure your clearance and filter pans by sump position and depth in the oil pan picker; drawings are in the oil pan guide.