Well the shudder is bad fluid - 99.9% of the time. A switch to Mercon V will clear it up and dont forget to drain the torque convertor.
If your having harsh/quick 1-2 shifts then new 1-2 accumulators are an order, but I would replace then no matter what when you do all this.
The J-Mod is easy, all the work is getting to the separator plate. Drilling the plate is the easy part. I recommend new drill bits so your right on spec.
If you need help you can search the forums or PM me and I can go into detail and take all the tech outt of it. Really, its an easy project, you just making holes bigger in a metal plate.