Running well off the bike, just like pacing, takes practice. The fact is the more often you run immediately after cycling the more physically AND mentally confident you'll be in your ability to run off the bike.
Not every session should be a hard run, however. You need intense and frequent bike/run sessions.
Add your high intensity bike/run sessions in the last few weeks or months leading up to your key race, but limit this to once per week. Keep your other runs off the bike short (10, 20, 30 minutes) and at a relaxed pace. Do this early and often in the season to teach your brain how to conserve energy for the run, which will pay huge dividends come race day. Also, frequent runs off the bike will give you ample time to practice how to quickly get into run rhythm.