Due to IT Band problems I've scaled back my training to one long per week and a couple short runs. My knee feels 100% and I'm debating on increasing my training to 3 4-6 mile runs per week and an 18-20 mile run within the next week. My training program (Hal Higdon) for the next 2 weeks is very light and only includes an 8 mile long run. My confidence is low even if I'm physically ready for the marathon. Your thoughts on changing my training....

At 2 weeks to the start line don't even think about another 20ml run. Been there with ITBS and it's not fun and seriously frustrating. If you've been sticking to Hal you're in good shape, nice stready buildup and 3~4 18ml+ runs. Now is not the time for craming. Focus on rest & nutrition, the hard miles should be done and you should be tapering. Another long run will only increase the possibility of injury.
Think about you're upcoming marathon, plan your race tactics and "last minute" race preparation.

4th last week Peak mileage week including peak long run (~45mls with 20ml long run).
3rd last week 75~80% of peak training load (16mls long run)
2nd last week 50% of peak training load (13mls long run)
Final week 30% of peak training load (10km long run)
DO NOT INCREASE YOUR TRAINING WORKLOAD AT THIS STAGE.