This issue ever get solved? I have the same issue with a 1997 GMC Sanoma 4.3l 4L60E. Speedometer is off by 10 MPH at 70 and after driving a while it causes the trans to shift hard and code for p1870 which is a general trans component slippage because the truck isn’t moving as fast as it the computer thinks it is. Could this be a PCM issue or is there a DRAC box?