STUPID GFCI!

Begger

Get a Kill-A-Watt external meter.   Plug in the freezer TO this device and see how much current it draws.   If your LINE VOLTAGE drops too much from 'off' to 'on' you have another problem.  
These meters cost MAYBE 25$ these days.  

Some high current devices may have a large TURN ON surge.   If your freezer is on a 15 amp circuit, perhaps UPGRADE to a 20 amp circuit using whatever code calls for regarding WIRE SIZE.   Probably 12ga, but maybe 10ga.    

Find out what ELSE is on the same circuit.   And by ALL means replace the GFI breaker with another with the SAME ratings.    Breakers only last so long before becoming flakey.  

The penny in the ice idea is nice, but only shows you after it's TOO LATE.  

Begger

See my post on page #1.   
I'd recommend ANY home owner to purchase a Kill-A-Watt meter which reads voltage, current and computes WATTS and VA.     Plug the appliance under test INTO the meter which is plugged into the outlet in question.  
Such a meter is chump-change at about 25$

HofstraJet

apinion said:

Just wanted to close the loop and state that I finally, so it seems for now, got this issue with the GFCI tripping in the garage resolved.

I noticed the wire ran was already good to go for a 20amp GFCI, so I changed the 15amp GFCI to a 20amp and it hasn't tripped yet.  Its been over a month.

So we will never know whether the old 15A GFCI was bad or just inadequate since you went straight for the 20A. Oh well. At least the issue is fixed.