Won't Shift...somtimes

[PS3Camaro]

90 RS Automatic V6
I've had this car for only about 9 months the owner before me basically was a moron, since I've had it the firing order was ALL messed up, guy probably hadn't touched anything in years, just terrible, anyways, I got a good deal so I'm not fretting.

My problem is, it usually wants to go all the way just b4 redlining to shift, or sometimes won't shift at all, when it doesnt wanna shift it will get around 50k rpms and just start well, I don't know how to explain it, jerks my car, like I'm slamming on the gas then releasing it, over and over and over, just rocks my car like crazy. Althought I have noticed that when the car is running great, I tend to be at a light and check engine comes on and it's just "o crap" from there, when it goes off, it will be fine, but usually comes on only a couple min after that.

I was told that the tranny was rebuilt 4 yrs ago but I'm really doubting it. Also, the guy I bought it from also told me he just had all the oils fluids etc. changed right b4 I bought it from him, well, I went to change the tranny fluid and walla...what I think is a reenforcment bar to hold up the tranny is on backwards, and I can't take off the pan, my dad feels we can just get a jack and hold up the tranny while taking off the bar and putting it on right so I can get to the tranny fluid and change it, but with that poroblem in mind I'm guessing that since the crate engine was put in it about 4 yrs ago the tranny fluid has never been changed. Could this very well the the simple solution to my problem? It probably is, and I know that I should probably change it before asking anyone for help, but I would like other peoples ideas and expertise on what else it could be while I'm working on it.

Thanks

[wrightz28]

Often times, a problem thought to be with trans is really a motor problem. Check the ignition timing out and condtion of the plugs.

Any white smoke at startup by chance?

[PS3Camaro]

I just replaced the wires and plugs about a month ago, and no, no smoke.