LT1-Z

While i was driving today, i noticed when i floor it, or even do a semi-quick acceleration, going from 1st to 2nd sounds bad. (A4 by the way) It makes a grinding noise for a second and will shake the back end of the car. When it gets to 6k RPM, sometimes it will shift right away and go down to about 3k, but sometimes it doesn't shift and will slowly go down to 4k, then shift, then get moving again. It feels horrible, no get up and go at all. So i get home and decided to check the tranny fluid, it's a little past full. (i also checked the oil and it was super low so i added some) then i took it out again to test it, and after adding some oil it was a little better, but here's some other problems. My 2nd gear all the way at the back, isn't even a gear, it's more like neutral. I can tell it's wanting to grab a gear or something but can't so it acts like another neutral. THEN one more thing, when i put it in reverse, and the car is warm, it won't shift until i push on the gas and get the RPM past 1k or so. If i just slowly push on the gas in reverse, it'll go backwards, but chug along, like a go, missed the gear, go, missed the gear, etc...

After all that said....do i need a rebuild?

And in the .0001% chance of no, what else could be the problem?