You might want to check the codes again. There is no P1415 code for this vehicle.
The P1870 code is the death code for a transmission. It is a transmission component slipping due to a mechanical failure in the transmission. This means time for a transmission overhaul.
The surging is usually a result of a faulty transmission pressure control solenoid or debris in the valve.
You might be able to extend the life of the transmission a little longer by replacing the pressure control solenoid and flushing the transmission. After that, clear the codes and see if they come back again. I would expect the P1870 code to come back. Sometimes it will take a long time for it to come back due to all of the parameters that have to be met in order for the test to run.
Be sure to get those codes checked again and post the results for me. I'm thinking you might have a P1811 code, since this code is related to surging and harsh shifting.
Sunday, June 6th, 2010 AT 9:49 AM