Hi. My '93 has a giant flat spot at highway speeds. It's like from 1500-3000 when on the freeway only. When I am riding and let off the throttle to slow down, I go to accelerate again and there is a minor rise in Rpms and then dead throttle and then you are going at speed again. It's frustrating and hard on the rear end. Around town it is smooth and responsive. No probs. Can't recall when it appeared. I've been through the carbs and did the pair removal as well as the carbon tank removal. I've even heard heard that airflow rushing past the vent tubes can cause this but I tucked them under the belly pan. Any ideas thanks. Oh and I tried the air cleaner holes mod and it made it way worse. So I'm guessing it's an air or vacuum issue. But I triple checked the hoses and caps and put on new insulators. And installed a new fuel pump, filter, and diaphragm.