Deceleration misfire

[BadBrad]

Hi, All. I've been driving these pickups since they were new, but have one with a really odd misfire. It runs great, idles smooth, no hesitation or hiccups. Until you're going downhill. Cruise is set, constant speed is smooth. Come to a descent, as soon as the throttle is reduced, engine starts bucking and missing. As soon as power is called for, it flattens right out. If you tap the brake to kick cruise off, or remove your foot from the pedal and coast, no misfire. Anyone else run into anything like this? 1996 K1500, 5.7 auto, 136K. Thanks for any insight!