Help with coil over

[Alexdwthunter]

Just fitted stance coil overs on my 6.1 got a nice ride height and handles good but if I hit a bump,or pot hole it feels like I’ve fell in a hole on the rear any ideas on how to stop this please

 

[Howzat]

Wheel/tyre combo.

 

[Alexdwthunter]

20inch wheels and a 255/35/20 tyre uniroyal explorer 2

 

[doncarlyon]

The low profile tyres won't be helping

 

[Alexdwthunter]

I’ve found out what’s up with them, the garage that fitted them have fitted the rear wrong so need changed contacted stance and told me to check a few things so back to the garage I go