Ok so the t-slim should give you an occlusion alarm if insulin isn't being dispensed correctly at the infusion site so if there is a build up or kink then the pump alarm should let you know to check tubing and set to correct this, if you're levels are erratic this could something like poor site absorption or insulin is going off.
I didn't get on with plastic sets myself but for different reasons, lumps and sore site with using plastic, can you try the sure t set instead which is steel tip, your DSN should have a few spare you can try, will help you to discount issues with the autosoft then ?