Rob, last time I checked, the IceCap 430 was only able to power 2 48" bulbs. Try rewiring for 2 and see if that fixes the problem. In the mean time I'll look for a reference for my statement....
No, you can run it either in a 2 bulb, 3 bulb or 4 bulb configuration.

2 bulb: 12' of lamp length (max) (2 at 6', 2 at 5', 2 at 4', or 2 at 3')

3 bulb: 12' of lamp length (max) (3 at 4', 3 at 3', or 3 at 2')

4 bulb: 8' of lamp length (max) (4 at 2')

For a 3 bulb combo, your on the maxiumum allowable. Try increasing the wire gauge on the jumpers as mentioned. The smaller gauge jumper could be causing the internal thermal switch to trigger, causing the ballast to shut down. Is the jumper wires the only wire you added on your own? Are you still using the OEM wires from the wiring harness?