Gen 2 Prius not charging HV batteries over 34 mph

This is my first post. I have a 2009 with 250,000 miles on it. This is a project vehicle at this point. I purchased it for commuting from Los Angeles to Northern California twice a week. This worked out great. I have replaced the coolant pump a few times but beyond that it uses a bit of oil but it has been great. I have since moved to Austin. I was on a 600 mile trip from Austin to El Paso TX and my HV battery stopped charging when the vehicle is traveling over 34 mph. This made for a very long trip back from El Paso but seems like there is a relay or fuse that blew. I thought it was the inverter at first but it charges the batteries normally under 34 mph. I did a test on the batteries and they are all fine. Any ideas what this problem could be? There are no codes and no Triangle of death.