Have you tried running at the same revs as 83 mph in top in a lower gear to see if it revs or speed related. I know the engine will have more load on it at 83 mph but it might show something up.
Could the vehicle speed sensor be on the way out? It might be struggling to give a good signal at higher speeds and this might be confusing the ECU. Also there is a good chance the cruise control will use the same VSS.
|