[sowise]

Might help to know what they did do for $2000. Also, might help to know the history of your exhaust. Your signature mentions you have a stebro set up, nice! pricey too. You also have headers as well. Is your Cat stebro? How long has this set up been on the car. Also if you have exhaust leaks it can throw codes for O2 sensors. so definitely want to check where the headers connect to the center pipe or CAT. Or even at the headers to the block. You are lucky in a way that you have the OBDII SVX but unlucky in the fact you have 3 O2 sensors.

My basic suggestion would be as follows:
Check wiring for recently replaced sensor (check brand too)
Check for leaks while inspecting wiring.
Check for potential blockage of the cat, a search should turn up the temp ranges you should see using a temp gun. High temps could cause early CAT failure.

start there...