PET can be really stringy. Some folks can get it to print like PLA, but I’ve not been able to, it’s still stringy for me, so I just print one part at a time. I’m running an E3d all metal hot end. 240C for the filament and 60 for the bed. 40mm/s for perimeters, 35mm/s for external perimeters, 55mm/s for infill. I have a delta printer though, so I can get away with faster speeds. Retracts are 2mm at 40mm/s. I’d go with what Ryan suggested and just slow down, you may, or may not need a new hot end, but if it has a plastic liner, check it every now and then to make sure you’re not melting it.