Whether you keep full coverage, which typically means state liability plus physical damage coverages of collision and comprehensive, on the truck while you sell it is a personal decision.
If you own a car outright and are not paying on a loan or lease you usually can have as little as the state minimum liability requirements or as much extra coverages as you like on it. If you have a loan or lease on the vehicle, it is likely that the lien holder will require the coverage to remain until the title is transferred.
If you feel comfortable taking collision and comprehensive coverages off of your truck while you sell it then your agent should be able to make this change for you. Without these coverages though the vehicle would not be covered for damage to your car when if it hits, or is hit by, another vehicle, or other object.
Your insurance would also not cover incidents other than collision. For example, comprehensive insurance covers damage to your car if it is stolen; or damaged by flood, fire, or animals.
I personally know if people who have had their car stolen when they have had it up for sale and had taken comprehensive coverages off the vehicle so were not covered for the theft of their vehicle.
Once again it is a personal choice if you should keep full coverages on a vehicle while it is up for sell or just place the state minimum car insurance coverage on it. If you are selling your truck and going to replace it with a different vehicle you can obtain an affordable auto insurance quote here with us.