Could a gas pipe obstruction could be causing a reduction in gas pressure to my furnace?
Did your HVAC tech disassemble any of the gas supply piping, specifically directly upstream of the furnace control valve/regulator? Any obstruction caused by debris (and yes, this is very possible) is very likely to be at the small orifice(s) associated with the furnace control valve/regulator than at other areas of the gas piping, which have significantly larger bore.

Built-in gas appliances should have a "drip leg" debris/condensate trap just upstream of the appliance: