Harsh, Soft, Delayed or Slipping Second or Sixth Gear

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2011 GMC Yukon XL, 2011 GMC Yukon, 2011 Chevrolet Tahoe, 2011 Chevrolet Suburban, and 2011 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

Checks	Causes
NOTE: On cold days, approximately 32°F (0°C) or colder, the transmission is designed to shift differently. The transmission uses a warm-up mode shift schedule until the engine reaches normal operating temperature. While the transmission is in warm-up mode, it is normal for transmission upshifts to be delayed or held longer. This feature improves heater performance by giving quicker vehicle warm-ups.
A/Trans Fluid Pan Assembly (29)	Verify proper fluid level and condition, inspect transmission assembly for leaks.
Control Valve Upper Body Assembly (304)	Inspect for sticking, damaged or worn 2-6 clutch regulator valve (334) and spring (326). Inspect for damaged or sticking #6 ball check valve.
Control Solenoid (w/Body and TCM) Valve Assembly (314)	Pressure Control Solenoid 4 commanded/failed LOW (off) or leaking - Perform solenoid valve assembly function test. Refer to Control Solenoid Valve and Transmission Control Module Assembly Solenoid Performance Test . Incorrect or inadequate adapt activity - Perform Reset Transmission Adapts procedure.
Center (with 2-6 Low and Reverse Clutch) Support Assembly (67)	Inspect for proper installation of the 2-6 clutch return spring retaining ring (455). Inspect for damaged 2-6 clutch piston assembly (457), spring (456), retaining ring (455), and center support assembly (459). Inspect for worn or damaged 2-6 clutch plates (451-453).
A/Trans Fluid Pump Cover Assembly (219)	Inspect for damaged, stuck, sticky pressure regulator valve (233) and springs (234 and 235). Inspect for damaged, stuck, sticky isolator valve (236) and sleeve (237).
Center Support Fluid Passage Seal Assembly (20)	Inspect for worn, cut, or damaged seals. Inspect for proper seal (20) size (6L45/50E MYA/MYB) vs (6L80/90E MYC/MYD).