Two low-cost or no-cost things to consider. I know you said you've tried different tires, but a good tire makes a big difference. I'd go with a 28m at 115 psi. The other thing that might help would be to shorten your handlebar so that your arms are pointed straight ahead (instead of slightly splayed as most stock flat bars do). Just cut off an inch or two from both ends. I assume you're using bike shoes/pedals. You have a nice bike and to get faster maybe pay attention at how you're riding. Many hybrid riders mash more than they should and do not pedal in a fast cadence. You'll notice road bikers' feet move faster. take advantage of your gears to maintain a quick consistent cadence.