My 2007 Elantra 5-speed hiccups when I shift a little too early (i.e., 18 mph instead of 20 mph) into 3rd gear (similar behavior in other gears sometimes). This is especially pronounced when rounding a corner or driving uphill from a stop sign. If I step on the gas too hard, I get a similar behavior until I reach a higher speed. I wonder if this has something to do with fuel delivery or ignition (or both?)
I ended up replacing my fuel pump assembly (because it was also mis-reporting the fuel level. The shuddering continued, so I've eliminated the fuel pump/delivery as an issue.
I bought a new coil pack and spark plug wires -- I figured I would just replace the spark plug wires first, since it takes less work. Voila! The shuddering went away. I also feel a bit more torque from the motor as well. Glad that simple fix solved the problem -- now to get a refund on the new coil pack... 🙌