I've had similar experiences. I would attribute it to either a change in lean body mass, i.e. more muscle tissue that could produce more heat when active or a change in brown adipose tissue which could be responsible for non-shivering heat production.

For myself it is likely a combination of the two. At a relaxed state, high temperatures (in low humidity) are no problem for me. But any sort of intense effort leads to profuse, instantaneous sweating. Waves of heat radiate from me year round. I also take much longer to cool off than most.

Like you I would attribute some of it to genetic heritage. I try to embrace it like using a lighter 50* sleeping bag when I climb and snorkeling without a wetsuit when surveying rivers. Having more or less body fat does have a slight effect for me. But the only time I've ever felt cold on a regular basis as an adult was following an extreme weight loss experiment which resulted in a huge loss of lean muscle mass.

no hard science here but a couple of thoughts....

It may help to have some herbs/spices like coriander, basil, fennel, turmeric, cardamom, and foods that are cooling and calming, sweet, bitter and astringent like coconut, carrots, leafy greens,cucumber, watermelon, steamed greens. Also try sipping cool (not iced) water throughout the day. And try to reduce spicy, salty, oily and sour foods such as chilis, pickles, and citrus fruits.

We can look to cultures who live around the equator that eat spicy food and wind up downregulating their body temps in some way. It seems like acute doses of spices foods will warm you up, but constant usage (think indian and mexican foods) may keep your body cooler.

You probably need more potassium. Try eating more foods with potassium like watermelon and bananas.

i can only speculate that your heart rate has gone done on the paleo diet and with the lower heart rate comes better heat tolerance. profuse sweating during exercise is normal