Intermittent Starting Problems

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I have a 2007 Chevy Colorado with a 3.7 liter engine. The problem started about 2 years ago when the starter went out. I had it replaced and then about 6 months after that it started having issues randomly not starting. Part of the problem is it's so random it's hard to reproduce the problem. There are time when you turn the key you get nothing like its a dead battery. If you jump it will start sometimes or if let it sit for 30 minutes to an hour it will start on its own. I finally had to drop it off at the shop and they had it for a week and said it was the starter. They replaced the starter and that seemed to help for a little while and then it started acting up again. doing the exact same thing. For a while it seemed like that something was getting hot and then once it cooled down it would start. Then it just started happening more often. I finally got it to act up for the mechanic and he claimed it was the starter again. They replaced the starter for the third time and the problem as returned. The mechanic and I are at a complete loss. There are no service engine lights or codes. when it comes to electrical problems that would be a weak area for me. I've had 3 starters in two years I replaced the battery I've replaced the battery cables Any suggestions or solutions would greatly be appreciated