Are these the original injectors? How many miles are on them? Injectors can suffer from several different problems. Carbon deposits on the nozzles, mechanical wear on the internal parts, clogged fuel inlet screens, wear on the pintle valves, bad solenoid windings, etc.. You might try doing a leakdown test on the injectors first to see if any of the pintle valves are leaking or otherwise malfunctioning. If the injectors fail the leakdown test, try using a good commercial solvent in the gas tank (such as Stoddard solvent) and see if that helps clear out the nozzles and free up the pintle valves. Chevron sells Stoddard solvent under the trade name "Techron" and is available at Chevron gas stations, most auto parts stores, and places like Wal-Mart, K-Mart, etc.. Try using one container of solvent in your gas tank on your next fill-up at the gas station and see if you notice any performance improvement as your tank nears empty.