2002 Aurora 4.0 trans lok problem

I have a 2002 Aurora with just over 140,000 miles on it and the transmission will not go into lock up. I have the engine lite come on and the fault takes place. WhenI clear the fault it will stay off till I accelerate above 45mph. I have changed fluid at about 80K miles and 135K miles and have been replacing with full synthetic. The pan has never been real dirty minor gray residue and vertually no metal on magnet. I had a crank position sensor issue at which I changed both units. I don't know which came first the crank sensor or the trans solenoid but when reset after replacement of crank sensor the trans solenoid is still an issue. Is this a replacement part?