When running on freeway all is well until I slow to a stop.It won't downshift or disengage and remains in high gear to the point it kills. So I unhooked plug on side of tranny.

Could be your torque convertor clutch solenoid, if you unhooked the plug and that fixed it, you need a new TCC lockup solenoid. $40 from dealer, +/- 2 hours labor to take the side cover off the transmission. Remove wheel on driver's side, remove side cover, replace TCC solenoid, replace gasket for side cover, replug trans plug, and you will be fine. If you're not mechanically inclined have a mechanic do this, as you do have to loosen one screw on the valve body and make sure it is torqued down properly when you're finished.