I missed your truncate because the indentation misled me 🙂

Try with CHECKPOINT command every several batches, because log cannot be truncated if checkpoint did not occur (also happens automatically, but we will force it here).

Also, you can optimize transaction log by setting large enough initial size (e.g. 4000 MB) and increment (e.g. 512 MB). Prior to that shrink log file to smallest possible (1KB). That will optimize number of VLF's in transaction log.