83 300D Transmission Shift Problems ??

Everything on my car works great except the auto trans and I am by passing that problem by shifting manually.
Question to you "am I doing any damage" by not allowing trans to shift automatically?
Right now, 1st gear shifts out quickly below 10mph, 2nd shifts at 18mph with a huge flair and 3rd shifts a little firm.
What I have been doing is keeping 1st in gear until 17mph (high revs)then manually shifting to 2nd and the shift is smooth as can be! Shift into 3rd manually is around 35mph (high revs)also smooth as silk and then we are off to the races and as long as it's in high gear it will run all day without any problem.
What is your take on what I'm doing as far as future problems being created.
If I am in heavy traffic or lots of stop signs and do not want to be shifting, I try to catch the shift to 2nd by slowing and the flair is almost negated.
Solutions??
Thank you,
John J

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