Baking in gas oven does not brown the top

I need advice from those who bake in gas oven without fan. My cakes get cooked darker on bottom and paler on top. Cookies can get burnt at bottom if I wait for them to change color on top. The result is that the cookies, puff pastry are not crisp, the sheet cakes are sticky on touch when they cool down. Really need advice from those who had faced and overcome this. Many thanks!