2005 ford mustang hard shifting?

So today I changed my oil, oil filter and fuel filter and started my car and everything it was fine put it in reverse and descending off my ramps everything fine no leaks. So about 2 hours later i go for a test drive and when i shift into reverse it like takes a second and then sort of jerks into reverse, i dont think anything of it.

so go for my drive and everything is fine, come home put it in park and then back to reverse and it does it again but never does it for drive.

so i go inside and google it and nothing good comes up and i read something where if you shift to N first then reverse it goes like butter so i did that and yes like butter.
do you think if i do that im doing anymore harm to the tranny or am i prolonging the life on it?

i have the 5r55s tranny it has 90k on it and had 61k i had a tranny fluid change. It never slips gears or anything and gets all scheduled maintenance. I do push her alot and do alot of 0-60 times. And like i said this is the first time it has ever happened and i didnt really think much of it until i read some horror stories online.
Added (1). if i just get a tranny fluid change do you think it would solve the problem, they do say to change every 30k?

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