i need/want a chip!!

i got a 96 deville 4.6 with 142k...i want a chip that improves horsepower and torque and can also maybe increase gas mileage at the sametime ( if that is even possible ).. i heard the "jet prom" chip is good and adds about 25 hp and 20 ft lbs, does anyone know of any that could add more gas mileage, horsepower, torque etc. and prices and availabilty? thank you all