trouble code P1870

Does anyone have a clue why I am getting a code P1870.
I know it has something to do with the trans.............but everything seems
fine. I really don't notice a problem in driving this 97 Lesabre. I will
mention there is a slow fluid leak somewhere(i believe it is one of the seals,cause it doesn't leak when parked) but I only need to refill about
1 pt/ 6 months. any help please!!!!!!

This code refers to percieved internal slippage which the pcm compensates for by bosting internal line pressure. Most times this is cuased by the tcc bore in the valve body wearing causing slippage on application. A full trans scan/diagnostic is the only way to pinpoint the problem.