I've got a 2012 with 114,000 miles on it. No tune. Engine is all original with the exception of the water pump, timing chain, guides etc. etc. all being done when the water pump was done. It surges up and down 200 rpm or so and misses at lower RPM and light throttle and just keeps getting worse. Replaced plugs and it made no difference. Plugs all looked nice when I swapped them out. It started off as a slight shudder which I initially thought was the tranny until it started missing too. No smells, no smoke, mileage hasn't really changed, no CEL. It does seem like it's down on mid-range power too off and on but still pulls hard above 4,000rpm. Not much to go off of I know. Where do I start looking?