If there is excessive friction material in the pan, new clutch discs and a band are probably a good idea. What will be more important is determining whether the wear is due to normal age and mileage or something else. If the vehicle has 150K of regular use it may simply be normal wear.
It is possible that the TPS can affect line pressure, thus affecting clamping force and the resultant bite or slip of clutches. However, there is also a pressure sensor array with limits to trigger codes if pressure is out of an allowable range. Further, the TPS affects a lot more than the trans line pressure, and will also trigger a code if its voltage is out of an allowable range. It would not hurt to scan the reported TPS voltage and/or measure it at the sensor, but I wouldn't expect that to be the primary cause of slippage unless someone has been ignoring the MIL for a long time.
While scanning the TPS voltage, also look at the transmission codes.