Hi. I have a 2000 Bravada that I’ve had forever but trying to give new life to. I don’t recall this happening before but whenever the rpm is over 2500 (going up hill or accelerating) the ac fan fades to off and comes back when less than 2500 rpm. This isn’t a vacuum actuated door s as you can hear the motor slow to a stop when it happens. The Bravada has the automatic hvac that holds a set temperature. Is this a feature to conserve engine power during high demand? Is there a way to disable it?