How do I tell a 4.8, 5.3, and 6.0 apart without opening them?

Don't count on eyeballing it — the 4.8 and 5.3 even share the same 3.78 in bore. Use the paperwork on the truck:

1. Glovebox label (Service Parts Identification): it lists the engine RPO code — the definitive answer. From 2018 on, it's a QR code on the door-jamb certification label.
2. 8th digit of the VIN: matches the engine code. Our engine table lists these VIN digits:

Liters	Engine	VIN digit	Years	Block
4.8	LR4	V	1999–2007	iron
4.8	LY2	C	2007–2009	iron
5.3	LM7	T	1999–2007	iron
5.3	L59	Z	2002–2007	iron
5.3	LM4	P	2003–2005	aluminum
5.3	L33	B	2005–2007	aluminum
5.3	LH6	M	2005–2009	aluminum
5.3	LY5	J	2007–2009	iron
5.3	LC9	3	2007–2014	aluminum
5.3	LMG	0	2007–2014	iron
6.0	LQ4	U	1999–2008	iron
6.0	LQ9	N	2002–2007	iron
6.0	L76	Y	2006–2010	aluminum
6.0	LFA	5	2008–2009	aluminum
6.0	LZ1	J	2010–2013	aluminum

VIN digits can repeat across different years and models, so always confirm the digit against the vehicle year — or better, the RPO code.

3. Heads can hint, not prove: 1999–2000 LQ4 6.0s had cast-iron heads (373/873 castings). See the heads guide for casting numbers.