Hi, 

I drive a 2012 Kia sorento crdi 4cly 2.2L diesel, and i think my torque converter is acting up.

Symptoms: 

1. Sluggish performance especially when driving up hills

2. mild reluctant gear shifting

3. Minor slipping when shifting gears especially on 5th and 6th gear, or when driving aggressively or climbing up hills

4. Rattling noise when decelerating

5. Non-linear torque/acceleration on gear 3 before it reaches gear 4

6. Symptoms are minor but can be felt when driving up hills or when car is being driven aggressively

The engine has driven 500,000 km on original, with no issues, no burning oil and no oil leaks. Engine serviced every 6500 km.

Gearbox has done 330,000 km.

I purchased the car 2.5 years ago from a used car dealership with 252,000 km, and that time i was abusing the car by driving it like a sports car and so the gearbox has failed (oil pump inside gearbox failure, so no drive). The mechanic replaced my gearbox with a 2nd hand including torque converter, which had done 90,0000 km on it. And ever since DAY 1 of gearbox replacement, the replacement torque converter had felt very weak and slipping. Most gearbox specialists could not find the problem that time because the symptoms were very minor. 

However, now i may be convinced that the torque converter is the culprit after having done some research.

Engine serviced every 6,500 km (approximately 4000 miles)

Gearbox serviced every 20,000 km (12,400 miles)

Engine age 500,000 km (310,685 miles)

2nd hand gearbox age 330,000 km (205,052 miles)

I've never had any major issues except replacing radiator, alternator, harmonic crank shaft pulley, AC compressor, 12v battery, and EGR valve during its whole lifespan.

The vehicle is used for Uber.