4th gear synchro failed at 13k miles

After having owned the car for not quite one year, and driving mostly highway speeds, the synchro for 4th gear completely failed. It happened on a day trip running errands around the city. After about 30 minutes of driving, I noticed that I would have trouble shifting from 3rd to 4th, intermittently. And by the time an hour went by the issue increased in frequency.

As my day was ending and I was driving home, I completely lost the synchro. To keep from grinding gears on a shift in or out of 4th gear, I had to double clutch. I took it to the dealership the next day, and they were able to verify the concern. The technician also noted that 3rd gear synchro was failing as well. The dealership replaced the transmission under warranty.

I live in the DFW Metroplex, which is a hot climate. With what I’ve been able to tell, heat is a factor in this situation. The issue started after I had been on the highway for some time, and I could feel the transmission tunnel was getting warm.