my 97 tigershark monte carlo has issues keeping rpm at half throttle. It works great at idle and full throttle. but if I try and hold half throttle on the lake it will go for about 5-10 seconds, then drop in rpm. A few seconds later if will recover and increase its rpm for another 5-10seconds. This happens during speeds between 25-35mph. I'm guessing this is fuel/carb related, but not sure where to start.