Mystery repeated extruder stall

Rooted K1 Max printing PET-CF (not PETG) which is a high temp filament with the best mechanical properties I’ve ever seen, and really high dimensional accuracy and no stringing.

The hotter the chamber, the better. 310C hot end, 110C bed. I preheat by setting the bed temp, raising the bed, turn off the exhaust fan and turn on the side fan and wait for 45C. Then turn OFF all fans.

I’ve had a lot of success, but was having some jams that have become constant making it useless. After the jams started, I converted to Unicorn hot end and replaced the 0.4 diamond Durozzle with the 0.4 unicorn, didn’t fix anything.

I have some prints where it showed a few layers of underextrusion that recovered, but now all my prints just stop extruding after a few minutes. I hear the extruder clicking

Now HERE’S the mystery part- upon stopping the print, I tried Extrude and it always flows JUST FINE! So… WTF? I had a theory that the panel’s Extrude used a lower speed that wouldn’t stall the stepper, except I used fluidd to extrude 10mm at 100 no problem. And I wouldn’t have expected to see a total stoppage if the extruder stepper was stalling. It’s total- once it stops, there’s no extrusion at all for as long as the job continues, but it extrudes easily outside the job. This makes no sense to me

I tried reducing the extruder temp. Added a heatsink to the extruder stepper. Reduced volumetric feedrate quite a bit in the slicer but nothing seems make any difference

The only thing I can think of is that the heat is making the filament too soft for the extruder to pull.
When you use Extrude, what temperature is that set at?
I use a fan that blows onto the extruder to prevent heat creep. works great.

Maybe try this.
https://www.printables.com/model/761891-k1k1-max-extruder-aquarium-air-cooler