Newbie Issues: Grace F9 with Micro Seiki DD-40

Hey all - total newbie here. I’ve only been researching phono setups for a few months. I ran into some serious playback issues after trying to replace my cart. Wondering if anyone can tell me what is causing it?

A friend actually gave me a DD-40 with original MA 505 tonearm (14 g effective mass) and stock headshell. So I have been thrown into this (awesome) world of hifi in an effort to live up to this amazing gift. The DD-40 came with a Stanton 681eee cart and I immediately replaced the broken stylus with an LP Gear replica as a placeholder before upgrading. To my ears it sounds really really good after calibrating it properly (I am an entry level digital audiophile but this is my first analog experience). 

Because my setup is MM for now I have fixated on the Grace F9 series as my first cart upgrade. I bought a used F-9 L on ebay from someone with great reviews and an easy return policy. The problem is the playback is absolutely horrid:

- distorted muffled sound
- incessant skipping
- needle gets stuck between tracks

I have recalibrated and readjusted many many times including starting from scratch and calibrating the entire TT and tonearm setup. Every time it still sounds the same. While doing the same steps but going back to the Stanton cart works just fine. I even replaced headshell wires and have nice cables (Kimber Kable and Van den Hul) and a Furman power conditioner. It’s running through the phono input of a Pioneer SX 838. 

When I increase the tracking force beyond the recommended range for the Grace the skipping issue gets a bit better but not really. And the sound always remains distorted and muffled - that never improves.

Visibly the cart, cantilever and stylus look totally fine meaning not bent or broken. But again I’m just a newbie and have not put anything under a magnifying glass.  

So all that said, with the issues I described above, what do you all think is the problem?

1) Worn out needle?
2) Bad / bent cantilever?
3) Busted cart?
4) Bad newbie calibration?
5) Cartridge / tonearm mismatch?
6) Something else?

Any help would be greatly appreciated - thanks!

YL