YL620-A VFD Problems

Hi guys, I am having an issue with my 1.5KW 110V water spindle attached to my quenbe Ultra. It seems to be seriously under powered compared to my Dewalt DWP611 router which is on my old OX CNC(leadscrew). When trying to use my 1" surfacing bit the spindle will bog down and stall if the DOC is any deeper then 0.015" at 100IPM 16000RPM. I can go way deeper with my OX CNC and the Dewalt router. I've also tried a 3/4 bowl bit at 0.0625 DOC 100IPM and it will also bog down and eventually stall the spindle. Slowed it down to 75IPM and still bogs down and stalls.

I've seen 2 videos of people running the same bowl bit at double my DOC and IPM with their Makita trim router.
I thought maybe there was something wrong with my YL620-A VFD so picked up a Huanyang HY01D511B VFD and still having the same issues. Both VFD's don't display any error code when stalling and using a kill-a-watt meter the amperage usually only goes up to about 3-3.5amps when stalling.

I've done a lot of vcarving with it the last year using a 1/4 downcut and 1/4 90 vbit at 150IPM at 1/8 DOC 16000RPM and have had no problems with it in that regard, even up to 200IPM but then cut quality starts to degrade. Tested the resistance from phase to phase on the spindle and they are all the same 4.5ohm so I think my spindle is fine but I'm no expert in that aspect. At my wits end here, searched so many forums and all over the internet. I'd like to start making some bowls and other things besides vcarving signs, especially considering Christmas is coming and I'd love to increase my sales.

Any help would be greatly appreciated!