GMC Sierra 2500 HD hard 3rd to 4th gear shift issue with towing causing jarring impact sensation on GMC Sierra 2500 HD

Some GMC Sierra 2500 HD owners report experiencing hard shifting issues from 3rd to 4th gear while towing, which can result in a jarring impact sensation. These problems may stem from the need for transmission re-programming and resetting the 3/4 shift TAPs. Additionally, low transmission fluid levels, a failing shift solenoid, or worn transmission oil filters could cause delayed shifts between gears. Some owners find that rough shifts are linked to incorrect readings from the mass air flow sensor during high RPMs, which can affect pressure and lead to late shifts. Testing with a bidirectional scanner may reveal that the transmission is attempting to call for third gear but fails to shift properly, resulting in a sensation of falling back into second gear when trying to engage fourth gear. Furthermore, the Allison transmission's behavior, which locks the converter and then unlocks when throttle is applied, can also contribute to this feeling. Proper diagnosis and maintenance are essential to address these issues and alleviate the hard shifting sensation while towing.