It sounds like your exhaust system is too open, and you have lost velocity of the flow of the exhaust gasses. An exhaust system needs a correct amount of backpressure to create the correct velocity needed for your engine to performance across all levels of its operating range. If you don't have a catalytic converter, I would consider installing one and a turbo muffler, I run a cheap [https://www.summitracing.com/parts/big-50052flt/overview/]Flowtech Raptor Turbo[/url] muffler. It is cheap, and has nice mellow sound when not on the throttle, no drone on the trail or when cruising down the highway.
