Cost on red is also not a big difference. With discounted toyota parts prices I can get a gallon of Red for $20 and change. Thats not a mix so when you go 50/50 it puts it at $10 a gallon. It is a bit harder to get on the trail.
I know Jason and I guarantee he did a proper flush including the rear heat. He is very meticulous about his work and procedures. You are going down a rabbit hole with this one pic diagnosis. If truck is running at correct temp then id keep going and have him check it at your next appointment.