Level kit, Check out Rough Country. I dont know if they make them for our trucks but I had them on my Tundra. Muffler swap, I just picked up a Hooker Max Flow should be installed this weekend. Just pocket the rest, those two things will run you about 500 with parts and labor. Good luck
I would go with exhaust and get a little more sound out of it. From there take your pick of covers for your bed. You have a TRX so, I would skip the level and just go right to a lift when funds are there for it (lift and tires).