Put a batch of TC on 7 days ago, usual formula that seems to work for me. Juice, tea, nutrient, kilo of sugar

big pre-prepared starter. It went of like a rocket, still has a 3" head on it but the gravity is still way, high by this time I would normally have expected it to be close to finished, last batched bottomed out at 1002 in 7 days.
Started at 1058, 7 days later, still at 1037. Any thoughts, like I say same process as usual, brew cupboard will be a bit warmer than usual but not much, I have checked my hydrometer and all seems fine. Any thoughts?