Transmission rebuild on Cadillac deville?

[Tina]

went to precision tune car repair because my check engine light on my 2002 cadilac deville came on. the car has around 70k miles.. i am the second owner. anyways.. the car was driving fine when i took it in. they told me something about the cyleniod needed replacement so i paid 5-600 to get that fixed. a week a later the check engine light came back on. so I brought the car back. they said everything looked fine and again a week later the light was on. this time they told me that I should just pay 2500-4k to get a transmission rebuild but i dont need it yet. they told me to ride with the check engine light on and once the gears start slipping to get the rebuild. I thought this was weird so i filed a complaint with the better business bureau thinking i paid to have them fix the cylenoid when i really needed the rebuild. to make a long story short they said they would credit the money spend on the cylenoid on the rebuild. but this is where it gets weird! so i bring the car in to get the rebuild and they tell me that after some test drives and a few second options at 2 differant shops.. they dont find it nessacary to do the rebuild!!!! they said the check engine light is off and the car is running amazing!! so i pick my car up and you'll never guess what happened a day later? THE CHECK ENGINE LIGHT IS BACK ON! im just getting really sick of this now! any ideas????