2003 Kia Sorento

Engine Performance problem
2003 Kia Sorento 6 cyl Two Wheel Drive Automatic 135000 miles

While driving around town the Sorento does great, but while I am on the interstate travelling 65-70 MPH, It seems to lose power and slow down, and will not accelerate. If I pull over and start up it does fine until reaching those speeds again. What might my problem be?
July 13, 2009.

I would check two things. First, make sure the fuel pressure is good. Here is a How to:

If it is good, have the catylatic converter checked to make sure it isn't plugging. Also, I am assuming that the check engine light isn't on. If it is, let me know.