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Q: Diagnose torque converter selenoid or transmission

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have an 06 avalanche 1500 ls 2wd 5.3 automatic that will drive fine for 30 mins then suddenly lose acceleration rpms still move but wont increase speed on road but once it cools down half n hr or so it will drive fine again no clicks or noise no shifting problems and it is not producing any codes at autozone the transmission is only 3yrs old fluid is full but has a hint of dirt to it but not burnt black or metal still red and full no leaks im not sure where to start diy cant afford to have shop repair can u give me ways to test if its the tranny torque converter or selenoid or any other ideas on diagnosis would be helpful please

My car has 200000 miles.
My car has an automatic transmission.

Hi there. The computer could be putting the vehicle into limp mode due to an issue that may be happening and reduces the engine performance. Check the battery, alternator, and all of the sensors on the engine and make sure that they are all working properly. If the engine is running normally, then there could be an issue with the transmission.

To check the transmission torque converter complete the following steps:

(1): Set the parking brake and start the engine. (2): Press down on the service brake and hold it on the floor (3): Put the transmission selector in the ’D’ (drive) position (4): Press down on the accelerator pedal to the floor for 3 to 5 seconds (5): While the engine rpm is high, monitor how high the rpm goes with the accelerator pedal on the floor (6): Let off the accelerator pedal and put the transmission in park (7): Shut off the engine and then release the service brake and parking brake

Make sure that when you perform this test, have your vehicle in a location where there is nothing in front of the vehicle to prevent any damage to your vehicle if for some reason the brakes fail during the test. It is best to add a pair of chocks to the wheels for added safety. If you need further assistance with your vehicle stalling for no reason after 30 minutes of driving, then seek out a professional, such as one from Your Mechanic, to help you.

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