The VSS is on the back of the transfer case. Look up between the parking brake assembly and end of transfer case and you'll see it and the 2 wire connector. You can unplug it and drive it to see if it makes a difference.
The ECU isn't the end of the world, plenty of good used ones available for reasonable cost. Swapping it out would at least eliminate it as the cause. From there you can check sensors with a DVOM to figure it out.
FWIW, I had a problem where my truck was running like it had jumped time and was dumping fuel into the engine. I checked every sensor, connection, and wire in the engine compartment. It turned out to be the ECU, and I confirmed it by swapping one from a good running truck.