Here are a couple of things to try...
If you're using a gas stovetop, make sure you're using a very heavy saucepan such as LeCreuset or a stainless steel pan with "sandwich" construction on the bottom. (This means there's a layer of copper sandwiched between two layers of stainless steel for heat distribution.)
This may work for both gas and electric stovetops (heck it's worth a try!) - use a flame tamer.
This device comes between the pan and the heat source and almost guarantees no "hot spots" in your saucepan.
If you're browning garlic, then pouring in tomatoes, etc., that could be your problem. I only saute garlic till translucent. I know Batali is fond of browning garlic but to me, it makes everything taste burned.
I know people are fond of simmering gravy until it's so strong it can take the paint off a Buick. I've never subscribed to that. I don't cook gravy past 1.5 hours after all the meat has been added. Extremely long cooking will evaporate way too much water out of your gravy and this might cause it to scorch.