July update: competed in another SCCA Majors at High Plains Raceway and finished second in both races. Temps were hot both days, but the first race was worse as my Z was overheating. Fortunately, one of my team found a small problem with the upper radiator clamp and after repairing that and getting out all the air, the car performed much better the following day. Used the same tires I had a LaJunta and that had my lap times off by a couple of seconds, so the leader (in a turbo Solstice GXP) put in a good drive to take both races.
Currently, the Z is in second place in the Mid-America Majors standings and in first with the Rocky Mountain Divisional Championships. My aim is to support all the races in my local area, and that means trying to concentrate on the 2020 RMDiv races. I've qualified for the SCCA Runoffs at Road America and have one more SCCA Majors to run In August, so it's time to buy some competitive tires.