Auto to 5 Speed Swap Question

[projectRDM]

Alright, you're getting somewhere. Is the neutral switch straight wired in? Sounds like it's giving issue if the bogging only occurs in neutral. Maybe you've got it going to the incorrect pin on the ECU. Unplug it too, see what happens. It's possible you've got it reversed with the 5th position switch.

The VSS would not cause issues though, as suggested above the injectors could be flooding the engine, but the ECU does not calibrate or tune based on vehicle speed, only by engine speed, throttle position, and airflow. That's a stab in the dark that missed poorly. You could be reading 300MPH, the ECU doesn't care, the sole purpose of the speed input to the ECU is to introduce the speed limiter, and to leg off to the ASCD and/or the ATC. It's not the VSS. In fact, unplug all the transmission switches and go one by one reconnecting them, you'll find the issue somewhere in there I bet.