You'd think it would be difficult to screw up a car shampoo, but some companies manage to do it.
Zaino Z7 is the best shampoo I've ever used. Duragloss 901 is also terrific and worth it if you have a Carquest auto parts close by. For the national brand stuff I like Meguiars NXT shampoo over Meguiars Gold Class, if only for the aroma. Mothers Calif Gold shampoo is also excellent and a nice, mild product which is good for those cars not disgustingly dirty. Eagle One shampoo is also very good, and can be found almost free with rebates and stuff.
No reason to keep using the crummy stuff. Just throw it out and spend a few bucks on a good shampoo. A jug of NXT or Gold Class is less than $10.00.