I probably should have explained with better details on how to arrange those Spark Plugs for their comparison Images. What I had in mind was to view them arranged so that they are like Six Guys standing in line at a Bus Stop... with the Camera positioned overhead to look right down into each Electrode Chamber... and compare them as arranged...1-6 and see which of them was either better or worse in the way of having Excess Carbon Deposits.. and likewise a view of them all from the side to capture the condition of their Platinum Coated Tips and the Gaps .
125 PSI is a bit low for a decent "Dry" Compression Test... and knowing which cylinder that Low Pressure was on might explain whether the same Coil On Plug was misbehaving. Your engine might be a good candidate for an ACDelco Top Engine Cleaner Soak to De-Carbonize the Pistons, the two compression Top Rings and the Upper Combustion Chambers as well, This will take Two Cans of this Stuff to be Done Right With the Spark Plugs Removed... Shake the Can well... and Spray into the Spark Plug Holes.
This stuff will initially Foam up quite a bit... and after an overnight soak... Pull the Fuel Pump Relay... and Turn the Engine Over two-three times for around 15 -20 seconds per roll and have the Spark Plugs Wells stuffed with Scott Blue Shop Towels... NOT regular Paper Towels or Terry Cloth Towels. If you fail to do this... and you prematurely put the Spark Plugs back in with this liquid stuff down pooling down inside of the cylinders... When you try to turn the engine over... the liquid TEC will cause the pistons to Hydro-lock the Motor... Bending the Connecting Rods and Ruining the Engine.
After this Black Goo of Carbon Mudd is evacuated from each cylinder ...Re-Install each NEW Spark Plug and Re-Install the Fuel Pump Relay before trying to start the Engine. If the Engine Starts... let it warm up for around 5- Minutes... and Do NOT race the Engine. Then turn off the Motor... And CHANGE THE OIL & OIL FILTER to the MOBIL1 Brand. A follow up Compression Test... Both "Dry" and "Wet" should be performed once the Engine is stone cold. This is the Only Stuff to Use to any real effect for the De-Carbonizing procedure:
https://www.amazon.com/dp/B007Q102AE/?tag=gmtnation-20