What are good slow sugar sources?

Unfortunately, I'm not sure right off the bat. I think the question should rather be about the rate of release of energy. Sugars tend to act and pass through our systems very fast, leading to highs and lows in energy whereas proteins take longer to be absorbed and thus not leading to roller coaster moods. Look for better resources on the internet to learn more.

fruits are good, the higher the fiber content in them the better, complex carbohydrates like oats, multi grains, etc. and veggies like carrots are very good as well

I think a better question is slow carb sources. I stay way from all sugar forms as much as possible. If 8 eat fruit its one that has a high fiber content like blackberries or raspberries. Or one that has natural binders in it like apple(pectin). Glucose is a dirty fuel source either way, but if the need is ther due to heavy or extended exertion, have a slow carb to limit insulin response makes much more sense.

Wholegrain cereals and rice are my favourite ones but pasta and bread are good too. They release sugar into your blood stream a little at a time because your body takes longer to digest them.

I participate in the "Bright Line Eating" food plan. I eat only fresh fruits, 12 oz. daily. 6 oz. with Breakfast, 6 oz. with lunch. All other sugar is restricted. Once detoxed from the sugar (s) you may have been ingesting, the cravings go away!