An intake manifold gasket leak on your 2013 Chevrolet Tahoe at 150,000 miles continues a long tradition of this issue on GM V8 engines. While newer generation engines are less prone than the notorious early 2000s Vortecs, gasket deterioration still occurs with age.
The GM Intake Gasket Legacy
GM's older Vortec V8 engines were infamous for Dex-Cool coolant eating through intake gaskets. The 5.3L in your 2013 Tahoe uses a different design but can still experience gasket failure at high mileage. The gasket seals both coolant passages and vacuum/air passages.
Types of Intake Manifold Leaks
Coolant leak - external leak visible at the gasket joint, or internal leak causing coolant loss without external evidence. Vacuum leak - air enters through failed gasket, causing lean condition and rough running. Some gasket failures produce both types simultaneously.
Code P0171 Connection
P0171 lean condition on bank 1 often indicates vacuum leak at the intake manifold gasket. The unmetered air entering causes the ECM to see lean fuel mixture. This code with coolant loss or visible intake gasket seepage strongly suggests intake manifold gasket failure.
Repair Considerations
Intake manifold gasket replacement is moderately involved - the manifold must be removed, exposing the gasket. Quality replacement gaskets are essential - don't use cheap gaskets that may fail again. The 5.3L is relatively accessible. Expect $500-800 for the repair at a shop.