Print is taller than nozzle while printing

[traxon]

CR-10S 300x300, e3d Titan Aero direct drive, Volcano, Keenovo bed, TH3D firmware, no part cooling fan (temporarily), 210 C nozzle, 65 C bed.

Just installed an Titan Aero. Seems very nice, but my printer is doing something weird I haven't seen before. It prints a few layers, which look fine, then the model increasingly starts growing taller than the nozzle for the rest of the print. Everytime it goes around, it keeps pushing the model down, and it starts getting quiet messy. I assume that's an obvious case of overextrusion, or is there something else? It's almost like the Z-steps are off or something. I did change from the stock firmware to TH3D, so, there's probably something I didn't set right. I greased the Z rods, but that didn't help.

I went through all the instructions I could find several times and don't see anything I did wrong. I updated the E steps to 837, then tweaked them to 818 so it was extruding exactly 100mm. I'm using Simplify3D and my extrusion multiplier is set to 0.90, and using all my previous settings, except I reduced the retraction to 1mm for direct drive. Any idea?

It's interesting watching it print like this, and I'm surprised it's not making a bigger mess than it is. It'll eventually be printing 1/4" lower than the top of the print, just moving things out of the way as necessary, like it's a floppy piece of rubber. I didn't realize the material (PLA) remains that soft for so many layers while printing. Makes me realize how important it is to not try and yank prints off the bed immediately after it finishes. (btw, putting the whole glass print bed in the freezer for 5-10 min works awesome to remove prints - falls right off)

I can post my settings or upload my .factory file somewhere if it would help, but I don't think I have anything weird set in my slicer, and like I mentioned, it was printing perfectly fine before the Titan Aero, with the stock CR-10S hotend and extruder, and original firmware. Probably something with the firmware isn't set right...