2003 Subaru Forester XS A/C Problem

The A/C is properly charged and has no leaks. Just had a new compressor put on as well. It will blow constant cold air all day long if you’re sitting still. Get on the highway, and you’ll have cold air for a few seconds, and then just cool air. Rinse, repeat. I’m hearing it’s just a crappy automatic climate control design by Subaru, but wanted to ask here to get more ideas.