TKR 88 GTA

Ok so first of all I know this has been discussed/debated so many times I tried searching for a specific answer and there is all kinds of mixed reviews about it.

I got an 88 trans am that's got about 127k on the tranny and I got the car back in 2008 with 103k. I didn't know what the service record of the tranny was so I didn't change the fluid in it because I didn't have any problems. Now I am having a few issues. If the tranny is cold/ warming up and I get on while shifting from first to second gear it sounds like it slips (tranny shifts and rpms drop but no pull for the next gear till about 1-2 seconds) after its warm it doesn't do it anymore. But if the tranny is hot or if I'm racing at the track it doesn't like the top of 2nd gear or idk but it won't shift into third at WOT at high rpm untill I left off the throttle.

So my question is top off the fluid in the trans because I know it needs some or doing a whole fluid filter change and all that. I know some have had problems changing fluid and filter and not having the tranny shift or shifts rough. Oh and by the way not quite sure but I think there is a shift kit in the trans because when I first got the car I was able to chirp the tires from first to 2nd. Anybody can back that up?

Thanks a lot any info would greatly be appreciated.