Hard to say without seeing the tire but generally, truck tires with sidewall cords showing are dangerous. If there is only a small groove in the rubber it may be OK to use. I see truck tires all the time with heavy cuts and scrapes from curbs on sidewalls.
If you take the tire to a store that sells them, they are going to sell you a new tire. If you take to a truck stop or truck tire center, you will prolly get a more accurate analysis.
While there, have correct valve stems installed while tires are off coach. The stock stems just don't work well with the wheels that are on our rigs. Valve stem extenders add an extra measure of risk and should be avoided (as you know).