Truck runs and idles great but knocks when decelerating

My SUV is a k1500 with 235,000 miles on the original engine. Mine makes a knocking noise only when I decelerate and the knocking gets slower the slower I go and only starts at like 20 mph. I have replaced the CV axles, u joints, plugs and wires, rebuilt the transmission, just rebuilt the transfer case because my chain was loose and changed the transmission filter, and put a new rear and on it. I regularly change my oil and even dropped the oil pan the last time and there is no metal in it. I am at a loss as to what it could be. I can grab the hook ups for my CV axles at my front differential and they have no up, down, side to side play. But I can turn each one back and forth about a half inch in each direction with the truck on the ground and the tires not moving. Any idea what it could be? It is loud enough for people to hear in a parking lot over my straight pipe exhaust. (3" pipe 5" tips with no catalytic converters or mufflers) which is embarrassing as hell. Sometimes it is worse than other times. I do all my own mechanic work myself and can do it all easily. I am just tired of playing process of elimination.