I have recently replaced a throttle body due to failed shaft seals. I took care when replacing the sensors to make sure they were installed properly. The car is a 98 GSX. I used DSMLink to log the TPS voltage with the car in the "ON" position carefully monitoring my adjustment to achieve .63 volts when the throttle plate is closed. When The car is started and idling, TPS voltage goes to .65-.67 volts. After a short drive and letting the car idle, TPS voltage reads .69 volts. I was trying to avoid using the TPS adjustment tool in DSMLink, but may resort to that. Once I get this taken care of, I can then focus on proper adjustment of the ISC. Have others had this problem before?

I've had that happen to me before. It almost seems like after you set the tps, you have to go for a ride and let it settle down, then adjust it again. After the second adjustment, usually it doesn't move any more

The car is on completely different voltages when not running vs running. This tends to have an effect of .2 volts. Either set it to .61 car off, or adjust it with the car on.

You said 'on position'. Try engine-on, running.