Chevrolet trucks coasting

[Bob] Having a problem while towing on a downhill grade. Truck while in drive seems to free wheel, not having any engine hold back effect, and I need a lot of brake, even down shifting does not seem to help. Not getting much help from dealers as to what is wrong. Any help would be greatly appreciated. Thank you.
Chevrolet trucks coasting

[John] It would probably be best to note what kind of truck, engine, and transmission types in order to better identify a possible solution to your problem.