1997 Dodge Ram misfire

My 97 ram pickup has a misfire, and I get code P0306. I changed plugs, wires, cap, rotor, rerouted plug wires in accordance with dodge tsb, swapped cyl # injector with cyl # injector, but stil have the number 6 miss throughout rpm range. It isnt 100% of the time, engine runs smooth a mile or so, then bucks and shudders, chk engine pops on, engine smooths out for a mile or so, then starts missing and bucking again, etc, etc. I check the codes, and its P0306 cyl #6 misfire. I do get a very occassional P0300, multiple cyl miss, but I get the #6 misfire code every mile.