94 Lumina not kicking into gear

I have a 1994 Chevrolet Lumina, 130,000 miles and I've been having problems getting it to kick into gear. I start the car and then it takes about 3 minutes before it will kick into a gear for me to go. Pushing the gas pedal doesn't help at all. When I start it, there is almost a hint of a clicking sound coming from under the hood of the driver side.

Transmission fluid was just added and all other fluids are fine. The coolant is not low although the "low coolant" light is on almost all the time.
Fuel injectors were replaced and many other things on the car including the coolant sensor and heater core.

Also, the heat is no longer blowing as powerfully as it used to. It used to blow out powerfully but now it's just silent.

What could it be? (We thought transmission fluid would help it, but that wasn't it.)