First thing is to buff everything's sheilds,armor, and health, because it's honestly harder to kill someone in MW3. Now to actually fix vehicles: Next is to give vehicles limited ammo, Dropships having the least, LAV's second, tanks the most. After that, make turret types having different ammounts of ammo, missiles having the least, rails second, and blasters the most. Lastly, Make different ammo types change vehicle speeds (misslis slowest, rails middle, blasters fastest).
This would make missiles strongest, but with the least ammo, and slowest, rails in the middle, and blasters having the most ammo, fastest, but the weakest. This would also keep Dropships from being Gunships.

And so it should be.

In MW3, you're a 30 metre tall giant robot, weighing anything up to 100 tons. If you're going to die this fast to enemy fire, there's something VERY wrong with your armour.

instead of that why not just introduce a rapid accelerating anti tank weapon. and put weak points on the vehicles . like a game that was out a while ago that was called fattle bield 3

Modern Warfare doesn't deserve the abbreviation. They can have MW4, but MechWarrior has a much better claim on MW, MW2 and MW3 than Modern Warfare.

So yes, we were talking about the wrong game.