What are the vents on rear of cab a 2003 GM Truck?

The vents on the rear of a 2003 GM truck cab serve primarily for ventilation and cooling of the engine compartment and/or transmission. They don't directly ventilate the cab interior. The exact purpose might vary slightly depending on the specific model and trim level. Some possibilities include:

* Engine compartment ventilation: These vents allow hot air from the engine compartment to escape, helping to prevent overheating.

* Transmission cooling: Some trucks have vents specifically designed to aid in cooling the automatic transmission fluid. This is especially important for heavy-duty trucks or those frequently towing.

* Exhaust venting (less common): In some rare configurations, there might be a small vent related to exhaust components, but this is less likely to be a primary venting purpose.

It's unlikely they're related to the cab's climate control system, as that is handled by separate vents and ducts within the interior.