* Transmission Fluid Level and Condition: Low fluid level is a very common cause of temperature-sensitive transmission problems. The fluid expands when hot, allowing for enough pressure to engage gears, but when cool, it contracts and lacks the volume needed. Check the fluid level *when the transmission is at its normal operating temperature*. Also, check the fluid's color and smell; burnt fluid (dark brown or black and smelling burnt) indicates significant internal damage.
* Transmission Fluid Pressure Regulator: This valve controls the fluid pressure within the transmission. A malfunctioning pressure regulator can lead to erratic shifting and gear engagement, particularly when the fluid is cold and less viscous. This is a likely candidate given the temperature sensitivity.
* Torque Converter Clutch Solenoid: This solenoid controls the locking of the torque converter. If it's failing, it might not engage properly until the fluid is hot enough to overcome the problem.
* Internal Transmission Problems: While less likely given the specific temperature-related nature of the issue, internal wear (worn clutches, bands, or other components) can cause shifting problems. However, internal damage usually shows symptoms at all temperatures.
* Transmission Cooler: A clogged or malfunctioning transmission cooler could cause the fluid to overheat, leading to the symptoms you describe. This is less likely the primary cause, but a contributing factor is possible.
Troubleshooting Steps:
1. Check the Transmission Fluid: This is the *most important* first step. Check the level and condition as described above. If the level is low, add the correct type of ATF (Automatic Transmission Fluid) specified for your 4T60E transmission. Do *not* overfill.
2. Inspect the Transmission Cooler: Check the lines leading to and from the transmission cooler for kinks, clogs, or leaks.
3. Professional Diagnosis: Since this is a temperature-dependent issue potentially affecting multiple components, a professional transmission mechanic is highly recommended. They have the diagnostic tools (scanners) to check for internal codes and pressure readings, allowing for accurate diagnosis. A simple fluid and filter change may address the issue if it's just low fluid or slightly contaminated fluid. However, more involved repairs are likely if the problem is internal.
Do not continue driving the vehicle extensively with this problem. Driving with low fluid or a malfunctioning transmission can cause significant internal damage, leading to costly repairs or even a complete transmission replacement.
