The test may be the issue as it decreases your collagen synthesis by a vast amount so when you damage your tendons during heavy training with weights the recovery rate can be as low as 1/5th of the normal rate but your muscles will continue to grow applying more stress to the tendons. This is why it is common to see steroid users with tendon ruptures or injury.
As far as I am aware a 2:1 ratio test/deca (within reason is most common) around 600mg test / 300mg deca.
Maybe try a combination of glucosamine, chondroitin and MSM, even though this is for joints it does help the connective tissues, anti-inflammatory meds or Cissius could do the job