Harsh, Soft, Delayed Or Slipping 1-2-3-4 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 1-2-3-4 clutch regulator valve (337) and spring (326). Inspect for damaged or stuck #1 ball check valve.
Control Solenoid (w/Body and TCM) Valve Assembly (314)	Inspect for contamination or debris. Pressure control solenoid 5 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. Line pressure control solenoid incorrect pressure.
1-2-3-4 and 3-5-R Clutch Assembly (51)	Inspect for damaged 1-2-3-4 clutch piston (414), piston housing (417), spring (413), and dam assembly (412). Inspect for cut, worn, or damaged 1-2-3-4 clutch piston seal (416), inner seal (423), and housing seals (424 and 425). Inspect 3-5 reverse clutch housing for cracked weld. Inspect for improper selective 1-2-3-4 clutch backing plate retaining ring (429). Inspect for damaged 3-5-R clutch piston (421), apply ring (405), and spring (420). Inspect for cut, worn, or damaged 3-5-R clutch piston dam O-ring seal (418), inner seal (419), and outer seal (422). Inspect for improper selective 3-5-R clutch backing plate retaining ring (400).
Torque Converter (with Fluid Pump) Housing Assembly (2)	Inspect for damaged or leaking 1-2-3-4 and 3-5-R clutch fluid seal rings (230).
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).
Torque Converter (with Fluid Pump) Housing Assembly (2)	Inspect for damaged or scored pump housing (203), cover (219), rotor (217), slide (212) and vanes (216).
Fluid Filter Assembly (26)	Inspect for damaged or restricted fluid filter assembly (26). Inspect for damaged fluid filter seal assembly (25) or improper sealing interface, leaks, and fluid aeration.
A/Trans Fluid Pump (Transfer) Seal Assembly (19)	Inspect for damage or leaks.