see if you can lift the outfeed table
Lift the outfeed table to see if it shifts under upward pressure. If so, tighten the gib screws a bit more.
When I set my roller supports for longer boards I use the longest straight edge I have, a 10 ft aluminum section. I slide the aluminum over to the first roller and if it hits, I lower it a bit. Another way is to lay the straight edge on the table, clamp it and sneak the roller up under it gradually raising it at the same time until it touches.
Did I mention I don't like roller supports?
You should also know that ripping a slightly curved board on the table saw will result in a repeat of that curve on the cut pieces. A straight line rip jig will almost guarantee a good edge on boards up to 8 ft long, at least in my experience. It's easier and faster than a jointer by far. If you can't get a 90 degree edge then, your blade is not 90 degrees to the table... it's that simple. A good, sharp blade will leave a surface clean enough for gluing, but you will need 90 degree edges.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)