[Bigdav160]

Does the truck back up? Then it's not the torque converter.

The indicator is controlled by a switch bolted to the drivers side of the transmission. If someone tried to unplug the electrical connector the switch is likely now broken.

If it will not forward have you pulled the shifter all the way to manual low or second? If it doesn't move forward in any shifter position I'd say the forward clutches are toast or the forward sprag is bad. (not that common)