One thing to know is the Venom Toxin, though a great ball, was introduced by Motiv before the introduction of their Fusion Pearl coverstock. The Fusion pear coverstock represents a point in Motiv's history where their coverstocks are now in the same ball park (in regards to strength and versatility) as other bigger ball companies. In today's Motiv lineup, the Venom Toxin is more light-oil than medium-oil.
The Venom Shock would be much stronger ball than the Toxin and would be quite a step up. The Shock would also have a similar shape to the Toxin (same core and earlier reacting and much stronger cover).
After saying that, I agree with the above in the Zero Gravity may be burning up causing carry issues. Altering the surface would my first adjustment along with a possible change in the line I played to help delay the reaction. The Zero Gravity has the ability to make a significant move in the back if the bowler's release allows it.