My wife likes to keep the tank just above E and last year it was hard to start when cold (big surprise), I have been filling with gas treatment at refills and replaced the plugs and cables last year but this week it started getting cool at night (40's) and the car has been hard to start. It turns over fine but just doesn't catch. If she releases the key too early then it really takes awahile to start. What should I be looking at next if not the plugs & wires? Only has 60k miles on it.