Have you checked your fuel pump?
I have seen fuel pumps fail on 80s that cause very low power and stumble at low rpms, sometimes under 3k. I have also seen fuel pumps fail that cause a failure at high rpm. It may be on its way out and causing...
I wouldn't want to scare you, but that radio lasted for about two weeks on my car. For less than 20 bucks it was worth the try, but it didntl ast sadly.
I've had both Trucklites and Holley Retrobrights. Having used proper LED replacements I highly recommend them over going high-end halogen unless you're going for a 100% authentic restoration. And even then, The Retrobrights look so correct that...