The best and only way to improve the acceleration and mpg is to hook the H3 to the back of an H2, put the H3 in nuetral, and relax. It works great.
Some have had issues with the K&N kits, some dealers have stated it will ruin the MAF sensor and void warranty, others have had good luck, B&B exhaust will help very little also. Other than that, there's not much out there to really make a huge difference. SC's and Turbos will give you issues and cause more issues off road.
This truck will never be like your Z was.
But it will crawl like a mult when you shift into 4LO.