Toyota Highlander, not starting in hot weather Options

[amyp]

2003 Highlander, intermttiently does not want to start, in hot weather. Happened on 4th of July. Used to happen last year, but we replaced the battery. One guy told me it was the alternator. His tester was defective, watch out for Auto Zone. Had it checked elsewhere, they said charging sytem was good. Had the big expensive service done on it last October. Drove it all day yesterday long distnace, and it was all good.

Read from another reader here thaat he took it to Toyota and they replaced a faulty computer under warranty. Wondering if I should do that, as it only has 47K miles on it.

Help, as it happened to the hubby twice. He suggested it was cheap gas, two weeks ago.. I filled it yesterday with Chevron, 91 0ctane.