Hyundai Repair: 2003 Sonata loses power, transmission control module, random occurrence

Question
While driving for 10 mins or more at speeds of 55 or more, the car loses power.  You push on the gas and you can see the rpm but it does not speed up.  You have to pull over turn off car and restart driving again.  This is random occurrence and can never be duplicated at the dealership.  Just took it in and the tech recommended replacing the spark plugs and wires.  We have replaced almost everything but the plugs.  I have lost faith in the dealership because I think that we are just shooting in the dark and hoping that this is the cause.  The computer did read a misfire and the engine light was on but normally the engine light does not come on!! Any other ideas?

Answer
Do the rpms increase like the car is in neutral?

If so, this is probably a transmission issue.  In that case, check the transmission fluid and check for any diagnostic trouble codes from the transmission control module.  If you find nothing amiss, you'll probably need to replace or overhaul the transmission.

If not, I suspect your fuel pump may be worn.  Fuel pumps often fail such that they produce less pressure as they get hot.  Usually, when this occurs, the car will again drive normally if it sits for a while.  This problem is also more likely to occur with a low fuel level because the fuel in the tank serves to cool the pump, which is also in the tank.

The second scenario happened to me once with one of my own personal vehicles about 35 miles from home.  I pulled off the road and waited for about 30 minutes.  Then, I started the car and drove to the nearest gas station and filled the tank.  I was then able to drive home without incident.