The thing that REALLY improved my endurance was doing full 5-section PT's. Since I had some money to spare, I bought pre-arranged 5-section PT's from Cambridge for about $9-10 apiece. They put in a section from an older PT into the selected 4-section PT.
@DumbHollywoodActor Read Pacifico's comment. It can be assumed that 7Sage's license just happened to be up for renewal before Cambridge. I have a feeling it won't be long before Cambridge will have to change their policy as well.
@Lumpkinmd
I would recommend 7sage and The LSAT Trainer by Mike Kim for starters. After you learn the fundamentals, Cambridge Drilling Packets will come in handy.
Now that you're done with the curriculum, I think you'd benefit most from taking PTs. Refer to the Cambridge packs and curriculum as needed for the question types or topics you struggle with most as you go along.