I've driven a manual transmission for most of my life. I'm thinking of
getting an automatic transmission in my next car. Once I was driving through
the rocky mountains in a rental car with an automatic transmission with four
speeds and overdrive. I shifted it "manually" while I was driving to get the
performance I was used to going up and down the hills, keeping to reasonable
speeds for each gear. I am wondering if driving an automatic transmission
that way will substantially reduce the life of the transmission? Does
shifting an automatic transmission manually while driving create
disproportionally more wear than when the automatic transmission shifts
automatically for example in stop and go traffic?

Thanks