For 1990-2009 cars

# 1-2, 2-3, 3-4, 4-5 Shift and Torque Converter Clutch (TCC) Characteristics During Cold Weather Operation on 4L60-E, 4L65-E, 4L70-E, 4L80-E, 4L85-E, 5L40-E, 5L50-E, 6L50, 6L80, 6L90 or Allison Trans.

Subject: | 1-2, 2-3, 3-4, 4-5 Shift and Torque Converter Clutch (TCC) Characteristics During Cold Weather Operation on 4L60-E, 4L65-E, 4L70-E, 4L80-E, 4L85-E, 5L40-E, 5L50-E, 6L50, 6L80, 6L90 or Allison® Transmissions

Models: | 2005-2007 Buick Rainier

| 2005-2007 Cadillac CTS, Escalade, Escalade ESV, Escalade EXT, SRX, STS, XLR

| 2005-2006 Chevrolet TrailBlazer EXT

| 2005-2007 Chevrolet Corvette, Express, Silverado, Suburban, Tahoe, TrailBlazer, TrailBlazer SS

| 2005-2006 GMC Envoy XL

| 2005-2007 GMC Envoy, Envoy Denali, Savana, Sierra, Yukon, Yukon Denali, Yukon XL, Yukon Denali XL

| 2005-2006 Pontiac GTO

| 2006-2007 Pontiac Solstice

| 2005-2007 HUMMER H2

| 2006-2007 HUMMER H3

| 2005-2007 Saab 9-7X

| 2007 Saturn Sky

| with Automatic Transmission

This bulletin is being revised to add models and applicable transmissions. Please discard Corporate Bulletin Number 05-07-30-018 (Section 07 -- Transmission/Transaxle).

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.