So you have replaced one or both, the dryer's heating hi-limit thermal overload fuse and the thermostat located on the side of the element housing. After a week or two, one or both of them have gone 'south again'. Do not allow this to upset you too much. Don't over think it just yet, it's not always a larger underlying problem.
I think those sensors are 'all' just made cheaply. Apparently the probabilities of getting one that slips through the quality control cracks may be somewhat high. I have replaced a couple myself in times past that did likewise. However, after replacement a second time, I have not had issues in years.
So before you go digging deeper into technical troubleshooting and worrying too much about the issue, just try replacing the fuse or thermostat, one more time. This just might be the ticket to solving your issue.
-chris
