Triton v10 Gettin Rough

Ford F 250 superduty V 10 triton airconditioning auto.
I m at 120000 miles had the spark plugs changed at 110000 miles mech said the wires were fine. Cal worthington in Alaska, anchorage. My truck starts up fine sounds good for a minute then starts the low up and down idle alomost dieing thing. Tach says 800 or so. On the highway if I give it a little gas at 55 mph it shutters. What do I need done? Thanks for your time.