i had the same prob, mine was worst, i can't even speed more than 120kph, the car will became very unstable, once i reported, they said need to change the rear shock absorbers and the coil spring to more improvised version, after change, ok can drive fast, cornering i will say slight improvement, the skips is still there on uneven surface cornering, but to be frank when u go on highway at high speed the car will feel very soft, so when take highway long cornering from the most left side (speed lane) u have to hold the steering light, because the Elantra EPS is not good in putting proper weight to the steering, maybe only i feel so

, but for me after i pass above 160kph, my car is more stable because of the rear diffuser i have, it makes the car like stick to the road, hehe, but still the steering feel soft, so have to handle it lightly, my fren suggest to install anti roll bar on rear lower arm, maybe i might but not now, apart from that, it is a great car, good for touring at speed 120 - 140kph(stable mostly at this speed), very comfortable ride, regarding FC, like what civispoon claim, engine oil and the type of petrol u use makes allot different, DON'T GO FOR SHELL, it sucks, will make ur car under-power, i use petron and clatex, even on rough driving i can get 425Km untill my last bar started to blink and still push the car further to 10 - 15km before i pump oil, normal drive combine cycle, i can get good FC easily 480 to 520Km until the last bar started to blink, mine is 1.8, hope this helps
great to hear you get good FC. but for handling wise, yes i agree hyundai is very sucks on that dept...at first very hard to adjust coz need constantly put steering input especially when cruising on hways..but now ok a bit...for the rear suspension its a failure from hyundai, surely...coz evryone is feeling the 'skips' especially on corners...for me no need to drive really fast at each corner...its skips only if there is a small bump at the corner...if smooth surface, cornering is ok...but if u drive alone...if u have passengers and some uneven cargo in boot, now its hell to drive...really unstable...
so people say just install rear antiroll bar and engine strut bar...yes it will make the firmer on the road...i not yet install it....since i always drive alone...maybe when i get my bonus next year will plan to install it...coz when u drive with family u need safety...u can't drive slowly all the time...sometimes when it comes to emergency cases u need the car in really good shape...