[MBilal]

You see this line in every if statement u using &&
gPlayerClass[playerid] == ASSAULT && gPlayerClass[playerid] == SNIPER && gPlayerClass[playerid] == MEDIC && gPlayerClass[playerid] == ENGINEER && gPlayerClass[playerid] == SPY && gPlayerClass[playerid] == SPECIAL_FORCE

That mean player should be in all class to use that vehicle...
you need to change it to..
just do like this
if(GetVehicleModel(vehicleid) == 425 && gPlayerClass[playerid] == here add class name which u want.)
like this
if(GetVehicleModel(vehicleid) == 425 && gPlayerClass[playerid] == ASSAULT) that mean only assault class can use that vehicle .