98 svt 50,000 miles

Purchased the car around 36,000
Every now and again it will stall when coming to a stop.
Idles fine most of the time right at 750.
Sometimes it will drop around 500 and I blip the throttle.

Changed the intake recently to the pipe from BAT Inc.
with a new air filter.

Seems to be running cooler than normal now!
Used to run in the upper R and now it is in the N-O range??

Could this be the intake install?
The temp outside is around 90 F

Today the CEL came on with a 0133 code O2 sensor slow...
P0133 O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)

I cleared it, will see if it comes back.

I've changed plugs, wires, waterpump, brakes, tires/rims, oil every 3000, etc...

What else should I look into?

Thanks!