What I have had is a faulty batch of filament that I eventually threw out as the size was not consistent. I got a Vernier caliper out and measured the filament and it went down to 1.5mm where it should have been 1.75. The extruder was still turning but the filament was slipping as size was too small. I did the same as you did. New PTFE new print head. ensured the hot end was hot enough for the filament and even ensured there was not a draft blowing across the printer. (I now have sides I printed on my Finder to stop drafts etc which allows me to print filaments like ABS without a heated bed. PETG is easier to print than ABS as ABS has a tendency to warp and curl.)
What I have had is a faulty batch of filament that I eventually threw out as the size was not consistent. I got a Vernier caliper out and measured the filament and it went down to 1.5mm where it should have been 1.75. The extruder was still turning but the filament was slipping as size was too small. I did the same as you did. New PTFE new print head. ensured the hot end was hot enough for the filament and even ensured there was not a draft blowing across the printer. (I now have sides I printed on my Finder to stop drafts etc which allows me to print filaments like ABS without a heated bed. PETG is easier to print than ABS as ABS has a tendency to warp and curl.)