08 Ford Edge has a shifting problem!

I have an 08 Ford Edge with a shifting problem. Started with a shaft sensor (?) being replaced, then it wouldn't shift into Reverse right after that. Took it to dealer twice and they replaced the shifter the 2nd time, but no change. When I try to put it in reverse, it will not go into the right spot, then I have to move it forward or back a bit to get it just right. Before the sensor thing was replaced, it was fine when putting into any gear. But now it doesn't even click into the gears like it used to. I have to basically "fish" around for the reverse. Does anyone have any suggestions what might be going on? I am getting tired of them not fixing it. Should I take it to another dealer? Luckily it's still under warranty, so it's not costing me anything but having to get a cheap rental car! I love my edge and hope it's not a lemon! Any info would be greatly appreciated!!