without adding a lot of complication. At the same time, avoid the truck decoy issue.
You can NOT avoid any decoy issue. It's practically part of the game, and if you even removed trucks 100%, there will still BE issues of decoys, and it will never end.
Part of REAL WARFARE has ALWAYS had decoys BTW, so it's not that unrealistic anyway. This has been happening long before the first Egyptian Warchariots were ever mass produced, and is not going to stop any time tomorrow either.
Putting a hold-fire causes problems, because now your tanks risk letting a bunch of LOADED trucks zoom all around infront of it while immune to fire. I'd think that tank then DESERVES to die for letting those infantry unload right up to it free of risk, and BOOM, use a satchel charge on it. I'd be exploiting this mobility a hell of a lot, so you're opening more cans of worms here.
I don't have a problem if there is an option for HOLD FIRE ON WEAK TRUCKS option, but that will have to be implemented with an adjustable scale the user can select for how weak is really weak. Not to mention, any opponent who is SMART can counter exploit this in many ways.
I just see another way that it will make the AI far more stupid than it already is.