No, it's not.

When lifting the other character you are either taking an action, or you interacting with an object -- depending on your DM's rulings.

If the DM rules that the pile driver is an attack (which I'd argue it is), that would cost you an action, and you can only repeat it if you have movement and an action to spend on it. This assumes you've grappled them, and have an attack left.

If the DM rules you are use an object. If it wasn't an enemy, you'd only be allowed to pick it up once. Once you drop it (which is free), it is no longer a free action to pick it up again. Use An Object action:

You normally interact with an object while doing something else, such as when you draw a sword as part of an attack. When an object requires your action for its use, you take the Use an Object action. This action is also useful when you want to interact with more than one object on your turn. (PHB 193)

Since you can't lift someone and do something else, it might take a full action to lift someone above your head. Remember that a round is 6 seconds, dropping someone more than once (or twice if you have the actions for it) would take about that long. Moreover, really can't lift someone and jump while doing something else, so it could be argued it can't be an interaction and must be a "Use Object" action.

To rule otherwise would allow a free 5d6 damage without using any action, and that, while awesome the first time (and a DM may allow it once, by Rule of Cool), is game breaking.

The spell does what it says it does, and the condition (Grappled) does what it says it does. Victor is flung 10'.

The spell moves Victor 10'. Clear enough. Unless something would stop that movement.

The condition doesn't cause Victor to be immobile, it reduces his speed to 0'. He's not nailed to the floor or encased in carbonite, it's just hard for him to move of his own volition. Grab someone by the wrist with both hands: you've got them Grappled.

So, since nothing in Grappled says Victor can't be moved by an effect (and, in fact, as you mention it specifically mentions this effect as one that can move the victim out of the grappler's grasp) and the spell says it moves Victor, that's what it does.

As long as the effect of Thunderwave ejects Victor from Gary's reach, Victor is no longer grappled.

(As @MartinCarney rightly points out, if Gary's an Otyugh, even 10' may not escape Gary's reach!)