2003 Ford Ranger

I have a 2003 ford ranger with 71000 miles. Sometimes when I go to start it I get nothing, so I have to take off the positive battery clamp and repostion it. Then I get power to my headlamps and everyhting but have to wait about 5 minutes for my starter to get juice. Also sometimes when I am driving the power will start to cut out in my radio and then I have to shut it off and repsotion the clamp and go thru the whole process. I inspected my battery cables and dont believe that is the promblem. I am stumped please help. Thank you