storage start-up

my 2001 ford ranger xlt v6 4.0L was put into storage for about 18 months while i deployed. it was never ran until i came back. i started it only after changing the spark plugs and wires, drained and added new fuel, and a new fuel filter. now it runs only on 5 cylinders. i replaced the 1 fuel injector and it still runs on 5 cylinders. all 6 spark plugs are sparking. the engine ran fine when i parked it. now it doesn't rev up past 3000rpms before it cuts out and jumps down roughly 500rpms before jumping back up to 3000rpms when i hold down the gas pedal. after roughly 10 minutes of running it starts to backfire from the exhaust and bog down even further. there are no smokey emissions from the exhaust.