98 Isuzu Transmission

I finally got the transmission fluid checked and am planning to do a flush this weekend, but I am not sure this will fix the problem. Before adding a quart of fluid it would slip and then jerk real hard when shifting. Now it shifts at the correct RPM but it still jerks real hard and there is a rattle just before it shifts. I am thinking something is broken inside there and am not sure if it is worth the $ to repair. Any ideas?