Throttle Position Sensor

I have a '98 with the 5.7 and auto trans. When cruising along at highway speed I could let off on the gas and within a few seconds the trans would down shift and start to slow down. But, out of the blue it will stop downshifting and just coast. This will last say for a week or so then it will start downshifting again. This happens with or without the Cruise Control on. Could this be the Throttle Position Sensor, and if I had someone pull codes would this showup. Thanks.

That would be a good start.
Also check trans data and codes while you are at it.
But the only real true way to test a TPS is on a lab scope.
They can have a glitz or drop out that will not show up on a scanner reading or volt/ohm meter.
MT-2500