anyone know what keeps the rear upper seat portion in place? having trouble removing mine

 You should be able to remove the 2 lower attaching bolts and lift vertically up on the seat as there 2-3 hooks on the back side of the seat holding it in place.

Don't see any lower attaching bolts, looks as if seat should slide up vertically but no go. Any other suggestions?

It has been a while since I took mine out but here is my suggestion. Take out the seat cushion. This has two bolts just where the carpet meets the seat bottom, you have to push back and up as I recall. The seat back is on with 4 hooks, two up and two down. I think you push up and out to release the lower hooks and then the top ones are similar motion. I remember having a battle with it too.