Hi dm-soundman,
If you are actually getting zero airflow, the ducts will need to be inspected to eliminate pinch points or other things that might be obstructing airflow.
If you mean the airflow is poor and the air is luke warm, that's pretty much typical. It's quite a long run from furnace to garage. Many people put portable heaters in the garage to supplement.
If you do get a portable heater, a ceramic disc heater is a good choice. Make sure you get one that has tip over protection. The
Classic Pelonis works very well, has tip over protection, and has a smart thermostat that reduces power consumption.