Harsh, Soft, Delayed Or Slipping 4-5-6 Shift

WARNING: This page is about a different car, the 2018 GMC Yukon XL, 2018 GMC Yukon, 2018 Chevrolet Tahoe, 2018 Chevrolet Suburban 3500 HD, and 2018 Chevrolet Suburban. 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 #3 and #4 ball check valves.
Control Valve Lower Body Assembly (307)	Inspect for worn, damaged, or sticking clutch select solenoid valve 2 (352) and valve spring (353).
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.
4-5-6 (with Turbine Shaft) Clutch Assembly (56)	Inspect for cut, worn, or damaged turbine shaft fluid seal rings (442). Inspect for damaged piston (439), piston dam (437), dam retaining ring (436), and clutch spring (438). Inspect for damaged or worn 4-5-6 clutch plates (432 - 435). Inspect for damage or leaking clutch housing (441). Inspect for improper selective 4-5-6 clutch backing plate retaining ring (431). Inspect for damaged or distorted turbine shaft.
A/Trans Fluid Pump Seal Assembly (18)	Inspect for cut, leaking, or damaged seal.
4-5-6 Clutch (with Output Carrier Shaft and Dampener) Hub Assembly (58)	Inspect shaft for damage or wear. Inspect hub assembly (475), dampener (476), and apply plate (477) for wear or damage.
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).