2002 brake warning lights

It's a 2002 Astro. The Brake Warning Light and the ABS lights come on randomly and will stay on. Sometimes they reset when ignition is turned off, other times they don't. There seems to be no issues with the braking system, otherwise. I put new pads on the front about 5,000 miles ago. There's no noise, no shuddering, no pulling to one side or the other, and it stops fine. The brake pedal feels normal. It may go for days without any lights coming on, but then come on and stay on. My wife told me that she drove it today and it felt like "it wouldn't go". I drove it right after her and everything seemed fine other than the lights being on. Fluid is normal.

Any ideas?

Another thing I forgot to add. My wife also said that, at least once, while the brake warning lights were on, the air bag light came on and blinked for a while and then went off and stayed off.

Need some help here, this is one of our primary drivers...