Where does it call for 5w-20?
My manual says:
Use SAE 0W-20 viscosity grade for
the 5.3L and 6.2L V8 engines. Use
SAE 5W-30 viscosity grade for the
4.3L V6, and 6.0L V8 engines.
Cold Temperature Operation: In an
area of extreme cold, where the
temperature falls below ✓29 °C
(✓20 °F), an SAE 0W-30 oil may be
used in the 4.3L or 6.0L engine. An
oil of this viscosity grade will provide
easier cold starting for the engine at
extremely low temperatures.