eletrical

Chances are the generator is failing. You can verify that by measuring battery voltage while the problem is occurring. It must be between 13.75 and 14.75 volts with the engine running If it is low, that will cause numerous computers to become confused and do weird things.

If the generator needs to be replaced, you must replace the battery at the same time unless it is less than about two years old, to reduce the number of repeat failures. Since the '87 model year, GM has had a real big problem with their generators developing huge voltage spikes that can damage the internal voltage regulator and diodes, and interfere with computer sensor signals. The battery is the key component in damping and absorbing those spikes, but as they age and the lead flakes off the the plates, they lose their ability to do that.