I'm having the same problem with my 2001 Kia Optima SE V6.
I called up my Kia dealership (Auburn Valley Mazda in Auburn, Washington; GREAT people) and here's what I learned:
The part numbers for the items are as follows, as well as prices quoted from the parts department:
4262039051 SENSOR - INPUT SPEED - $120.12
4262139052 SENSOR - OUTPUT SPEED - $120.12
Now from "Kia Parts" - Kia accessories below wholesale
I was quoted $77.13 each.
I have yet to find out if this is a good fix, but I'm fairly confident it is.
Also, I purchased my vehicle 3/12/08 and didn't have a problem for 2 1/2 weeks. Found out that a preowned Kia has only a 50,000 mile 5 year warranty contrary to the 100,000 mile 10 year warranty they advertise.
Just thought that would help everyone!