I have a 2013 Hyundai Elantra Limited with 125k miles and an automatic transmission. The vehicle stutters/jerks before the transmission downshifts. The problem occurs when I am light on the throttle, cruising at a steady speed, and the engine load increases very slightly necessitating a downshift to a lower gear (e.g., very small uphill grade, accelerate <5mph to keep up with traffic, etc.). Before the car downshifts, it stutters/jerks repeatedly while I remain on the gas pedal with constant very light pressure. If I press harder on the gas pedal, the car will downshift and the stuttering/jerking ceases. If I keep the same constant very light pressure on the gas pedal, the car will continue to stutter/jerk until I let off the gas pedal. The issue most commonly occurs at around 38-44 mph (gears 5 and 6), although the stuttering/jerking has happened in lower gears with less severity and frequency.

Things I've tried:

• Changed the transmission fluid (Valvoline Maxlife Full Synthetic ATF) @ 119k miles
• Upgraded to an integrated fluid temperature sensor and internal harness (see Hyundai TSB 14-AT-010) @ 124k miles. This necessitated changing the ATF again (Valvoline Maxlife Full Synthetic ATF)

I don't recall when the issue first appeared. However, it was prior to the first ATF change at 119k miles.

The only OBD codes the car has are: C1205, C1208, C1211, C1260 (wheel speed sensor and steering angle sensor). I believe these are unrelated since they appeared after I changed the tie-rods and performed a DIY alignment. Otherwise, the car doesn't have any lights or codes.

What could be the problem?