Harsh, Soft, Delayed or Slipping First or Reverse 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 1-R/4-5-6 clutch regulator valve (327) and spring (326). Inspect for damaged or sticking #2 ball check valve.
Control Valve Lower Body Assembly (307)	Inspect for sticking, damaged, or worn clutch select valve 3 (352) and spring (353).
Control Valve Lower Body Assembly (307)	Inspect for sticking, damaged, or worn clutch select valve 2 (352) and spring (353).
Center (with 2-6 Low and Reverse Clutch) Support Assembly (67)	Inspect for damaged low and reverse clutch piston assembly (470), spring (469), spring retaining ring (466), and center support assembly (459). Inspect for damaged or worn low and reverse clutch plates (463 and 465). Inspect for damaged low and reverse clutch backing plate retaining ring (461). Inspect for damaged low clutch sprag assembly (467). Holding the sprag assembly with the retaining ring facing up, and the inner race of the sprag assembly fixed, the outer race should freewheel counterclockwise. Inspect for cut, worn, or damaged low clutch sprag seal (468).
Control Solenoid (w/Body and TCM) Valve Assembly (314)	Pressure control solenoid 3 commanded/failed HIGH (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.
A/Trans Fluid Pump Cover Assembly (219)	Inspect for damaged, stuck, sticky pressure regulator valve (233) and spring (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).