1999 ranger coolant problem

[iroc254u]

HI i am looking for some help. I have a 99 ranger i have been having problems with. First off i blew the side out of my radiater it has been real cold here 30 below. My problem is i replaced the rad cap and thermost. It seems like i have air in the system but i did brp it. It starts loosing power So i pull over and pop my hood and my overflow box is full and my radiater hoses are sucked together and when i release my cap the blow back out to where they are suppose to be. If i let it run in the am befor i take off with it for about a half hour it will work great and blow good heat with no problems. If i start it up and take right off is when it starts acting up not blowing heat temp needle jumping up and down so i pull over and pop the cap and will run fine. I have no fluid in my oil but do have to add coolent when it acts up. Anyone ever had these problems? Any help would be great
Thanks