The vehicle was purchased for the express purpose of towing a 6,600 lbs Travel Trailer. This truck is equipt with the 3 liter Diesel engine. While towing the truck computer counts down milage available based on Def level. The count down is not mile for mile it is an exponential count down. This factor triggers a series of warnings concerning vehicle operation and impending speed restrictions. 1000 mile DEF range warning is first up. Followed shortly there after with a 300 mile DEF range warning (700 miles had never been reached to trigger the warning). The next warning is ‘DEF Low (red warning) speed restricted soon’. Shortly there after a 500 mile count down starts for the first impending speed reduction to 65 MPH max. This is followed by other speed restrictions that will put the vehicle eventually into a 5 MPH speed restricted mode. When adding DEF to the tank the level has never been below 60% full. Its not empty as the gauge and computer indicate. With each filling of the DEF tank the range you can drive is less and less until the truck is driven without the trailer hooked up. GM has a service bulletin for this situation that has been in place since September 23, 2024 and no permanent repair of solution has been prescribed. During the 500 mile count down to the first speed restriction the instrument cluster is locked out to only display ‘DEF Empty’ and alternately the DEF range counting down. No other safety features are visible such as engine temp or transmission temp important to know while towing. I Purchased this vehicle March 17, 2025 stating my intentions to tow a travel trailer. The dealership no GMC ever made me aware of the Service bulletin of the DEF restrictions. Had they done so I would have purchased a different vehicle with out the associated travel issues. Please reference GM Service Bulletin #24-NA-196 Document ID 6736285. This document was given to me after my 4 visit to a GMC dealership to have the issue addressed.