2005 ford Mustang hard shifting? - 1

So my mustang last night made a jerk into reverse, I didn't think anything of it till it did it again. So now I'm a little worried it's got 90k on it and at 60k I replaced the transmission fluid but they put the wrong stuff in and I drove around for around a month with it slipping a little and then I got the right stuff in.

I was just thinking of changing the fluid and see where that puts me might make the transmission last a little longer, before I have to replace it.

Sorry this is a repeat question they keep taking it down for some reason.

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