With the exception of Betty my 120-491 none of the Kenmores we have has given us any real tension issues. Betty came to us totally seized up and every nook and cranny was packed with reddish wool lint. It took a lot of work to get her to sew at all, and a lot more work to get her tensions right.
When machines keep screwing up, it's usually operator error.
Thread will have some effect on tension and you'll have to adjust the machine accordingly. I found that out when using the C&C Dual Duty Heavy thread on my "All Machines Quilt".
Joe