Sonata transmission overdrive

Its a 3.0V6 tranny , shares the same tranny with a 3000GT as per the manufacturer.Anyway , my tranny works well with the o/d off but when i engage the tranny , (o/d light off) the car feels like it goes into neutral.

Could my TCM be bad or is it mechanical failure in the tranny,I tried to override the cruise control circuit and by pass it to the TCM, just keep blowing the fuse. (o/d circuit goes thro the cruise control with cars that have the cruise control) .....Any ideas welcome! ..