Does NTST never go high? I believe when you are away from the top slowdown magnets, you should have G24 at con3-4 on 188e. If you don't, trace it back to NTST travel cable #22 to CWI board con 400-6 to 400-6 on selector. If you are out of the slowdown mags and have no G24 on selector con400-6, but do have G24 coming in to selector on con400-2, you probably have a bad selector board. I would guess the sensor on the aux sensor board but it goes through the main sensor board too. And if NTST does not change state in IMS when conn3-4 is grounded, 188e input is bad. You can move it to a spare input.

Ok Txs. Do I need Lon tool to move to spare input ?

No just IMS

You mention checking the magnets and they look fine. But... It doesn't take but maybe 1/16" gap between any two magnets and your description of slow speed up is what your gonna get.
It's easily overlooked at the bottom because you can't twist the tape around like the top to view it.

On moving I/O's, I believe the field CONN wire as well as the I/O need to be changed to that spare location.
If your using IMS you can record the up run, play it back and see which inputs are dropping out at the improper time.