bogging 66 gt5

ive done the following to my motor gasket matched,hogged out the muffler ported both sides of the int.and exhaust and ive had to put my clip on the second notch from the bottom to get it to run.good on mid and top range,but when my motor gets hot it boggs bad on low end? and its only got around 200 miles on it

my plug is a greyish to brown color i think its a lean bog.it runs great when its cold after about 15 mins it starts losing power ans start bogging at low end