P0455 trouble code

P0455 - Evaporative Emission Control System Leak Detected (gross leak)

Also can be caused by a loose gas cap.

For the shudder, if this occurs around 35 to 45 mph, and only after the engine warmed up, when it occurs, hold road speed and the accelerator pedal perfectly steady, then lightly tap the brake pedal with your left foot. If the shudder stops for a few seconds, then starts again, it's caused by the lock-up clutch in the torque converter. It's trying to partially lock, breaks free and slips, then tries to lock again, repeatedly. The fix for that is to do a standard transmission fluid and filter replacement, but you must use the specified transmission fluid. Using fluid that doesn't have the required additives is what causes that shudder.

The filter is not the issue, it's the wrong type of transmission fluid; a very common problem on most car brands. The only reason I stated it that way is for most cars, the common transmission maintenance service requires removing the pan to drain the fluid, and as long as you're in there, it would be silly to not replace the filter right away. Or, ... If you want to replace the filter, the only way to do that is to drop the pan to get to it, then the fluid runs out.

Be aware when doing this service, only about half of the fluid gets changed, but that is enough to get new stuff in there with the required additives. The other half of the fluid is hung up in the clutch packs, valves, and passages.

Be sure to verify this first with the brake pedal tap test. That initiates the release of that chattering lock-up clutch for a few seconds. If the shudder continues when tapping the brake pedal, there are other, less-common causes of shudders that should be investigated.