We have a 2001 Nissan Maxima. It's an automatic. For some reason, it's been giving us some problems shifting into gear. It's only happening intermittently; one mechanic couldn't find the issue, another ran a diagnostic and did a radiator flush. That shut off the "check engine" light, but the problem persists. I checked online and it could be electrical, mechanical, or gremlins. Anyone have suggestions or experience in these matters?