LEXMICK

Both my RX 300 and RX 330 are doing the same. When driving on a long uphill, I smell like a burning tire coming from underneath the vehicle. I am going fast at 65 MPH and don't have any acceleration problem. It's just the smell that annoys me and I have to roll down the window to neutralize the smell. The smell goes away when I reach the top, level surface of the hill. Can anyone tell me what's causing this? Is this normal?