2002 Santa Fe running rich
 

A very long story short:
My 2002 Santa Fe is running rich. It runs rough when you first start it up and after a couple minutes runs fine. Running it for extended periods leads to fouled plugs and burns up the catalytic converter. Allot of work has been done by the dealer and they said it needs a new computer or there is something wrong in the wire harness.
My local mechanic checked the computer and the error message says simply "transmission".
Before I spend more money on a ECU, I would like to rule out anything simple.
Any help would be appreciated!

Anyone?

someone?