running ruff with 0420 code

[double_u_4]

well i just got my truck back after having timing replaced. & the truck was running good for a few mins. but it started to run rough & chug. the exhaust was turning cherry red,it had a misfire. so we put in new plugs, wires,coil pack, crank sensor, & that seemed to work for about a day then it started to run rough again. if i am @ highway speeds just coasting its fine. but under any acceleration it chugs hard & seems like it doesnt want to go. i checked to make sure the wires were to the correct plug That checked out fine. it almost feels like wires are switched to the wrong plug but they arent. but now im getting a 0420 code. there is a small leak in the exhaust after the cat. it looks like the gasket isnt in all the way & about the last ft on the tail pipe has a bend in it. would those 2 things with the exhaust cause that big of a problem & make the truck run rough like that. the bend in the tail pipe has been there since i got the truck last year so i dont think that would make any difference,

 

[double_u_4]

so i was checking the wires again & i dont think that the wire for cyl. 3 is all the way on. it feels tight but i never felt the little click when i was putting it back on. i dont know if its because its such a tight space to get to. but if it doesnt click on will that make a difference. but i notice that it want to start the vibration @ about 2000 rpm under acceleration but goes away when coasting. also when i put it in reverse it seems to do it right away i feel the vibration throughout the whole truck. could it be something with the engine or ive been reading that also u joint could b the culprit. the only thing im wondering it was fine before the timing chains were replaced now that that was fixed its starting this vibration. it kinda feels like in driving on the ripples on the shoulder of the highway all the time

 

[double_u_4]

the vibration doesnt seem to be so bad when idling, but when i brake now it gets real bad when i am about to stop.