O2 Sensor Connectors -- help me Rhonda!

[geekdaddy]

I've got a 99 2.5 with 4 O2 sensors. I'm doing an IMS retrofit and pulling the exhaust.
Everything going well so far, except...

I'm struggling to disconnect the O2 sensor connectors -- the black ones with the burgundy colored end pieces. I looked online and seems that I should be able to tug on the burgundy end-piece and pull/slide it out to disconnect the connector. But mine aren't budging. I don't want to break them.

The vehicle is in overall great shape with minimal corrosion underneath and the connectors are in good physical condition. Again, appreciate any words of wisdom...