Did it draw enough air in the past to keep the fire alarms off? If so, what changed? Is it in a hood? Filter all cleaned, or is the motor slowing down so that it can no longer move enough cfm? Tell us more, if you have know more details.

it is in the hood and I think that the fan is underperforming because of the grease issue.
I sent out a general SOS to the parents in my class, and like always, most don't read the actual communications that I send. However, light appeared for me in the form of a parent calling me last night (he hadn't read his emails, his daughter told him) and offering his services. He is an EE who designs ventilation systems for commercial buildings and such!
I know that our club members include a ton of very smart guys who figure out most everything, so I know enough to ask for help when it is above me. I will find out more when we get up on the roof tomorrow and put the "Tricorder" on it.

From my experiences, the health department would not let us have a certificate of occupancy for a commercial kitchen remodel unless the hood venting system was capable of evacuating so many cfm. If yours was working and the motor is still turning freely at about the proper rpm, you probably have a maintenance issue, and probably need to clean/replace the filters, clean the grease traps, and clean the flue, cap, etc., of built up grease deposits. This would be good maintenance anyway to avoid fire hazards in the future. I can not tell you how many fire damaged homes I remodeled in the past because of grease build up in the hoods, on the cabinets, etc. One dentist seemed to burn his kitchen down on a regular basis for a couple of decades. He was a great client and had a really good ranch for hunting on. Let me know what you need and I will see if I can help.