After the latest update IVPack doesn't seem to want to play nice with Vanillaworks. If I install both of them at the same time I lose the ability to mod the Euros, Flash, Blista T/A, Dominator Classic (those are the ones I checked). Only other mod I have installed is Naturalvision Remastered. I dunno what's happened.
They work fine for me with IVPack installed. The vehicles listed in the ReadMe are the only vehicles affected by the whole ID thing, all of the other vehicles in the game have customization like normal, atleast in my game. Try moving your mods folder to your desktop, then create a new one and only install IVPack & VE. If it still doesn't work then I don't know what is wrong.
The issue was that I had installed the Simple Trainer support, it seems. I deleted my traineriv.ini and reinstalled it and now all tuning parts are working.
I've got that installed as well, no problems here. I really don't know what is wrong with them but glad they're fixed.