1997 Dodge Ram Voltage drop

On my 1997 Ram 1500, When the vehicle is in park and idleing, The volt meter reads 14 volts, When I have the lights on and put it in gear, the volt meter drops (Charge light comes on). My idleing RPM's is about 750. In gear RPM's drops to about 350-400. If I apply the accelerator and boost RPM's back to Idle status (in gear), Volt meter returns to normal. Is this caused by a bad TPS (Throttle Position Sensor). I have replaced the altenator and the computer containing the infomous V-regulator (good job Dodge).