Transmission does not shift into drive or any forward gears

Hello and thank you. I tried looking for my problem, but finally just asking.

Truck has been well maintained, worst issue is lots of wiring degradation, fluids have always been maintained but recently all of a sudden, the truck would no longer shift into drive. It goes into reverse perfectly and will drive in reverse but will not go into any forward gears. No other problems or work recently done besides new radiator hoses and an oil change. I had the transmission fluid flushed and changed last summer. Any direction or advice would be much appreciated as this is my main work truck, I use to feed my family.