Ok, John----the good: the muffler looks good. The detail painting seems ok--tools, etc.
Now to get to the things you could improve: first, whatever is the strange white powder on the model, get rid of that if you can. It's very distracting, and not convincing at all if you were trying to show dust. It's too sporadically-applied for that.
Gray vehicles are tough because that gray paint shade just sucks up light. You need to simulate the effects of light and shadow on a model to make it look realistic. First, if you want a simple thing to do, dry-brush this model with a light tan color. That will simulate a dusty finish, while highlighting and defining the edges and the shape of the turret and all the various projections on the tank.
Next, add pin washes with black. Use oil paint, and a small, fine brush. Make a puddle of diluted black oil paint, and use the fine brush to coax the mix into all the panel lines, around all the projections on the tank. Around the hatches, the engine grilles, the bullet splash rail, etc. Now you've got highlights AND shadows. This finish will come alive.
It's best to simulate scratches and wear with a metallic brown or grey, NOT silver. Use silver VERY sparingly--only a small percentage, maybe only on the edges of the front fenders where they might get bumped? But VERY lightly.
If you want to do some advanced technique, use your airbrush to add a lightened coat of paint inside the panel lines of the tank., Spray lighter gray on the inner panel--something like this. You can then mitigate the difference in tone with washes and filters. Then do all the above steps as well. 