Cooper04

I have a 3.4L V6 Toyota 4-Runner. I'm experiencing a loud engine roar, and sluggish performance. The gas pedal is also incredibly stiff. These symptoms happened after my former engine mechanic removed my right cylinder head to correct a cooling problem. I was wondering if you all have any ideas or suggestions of what could possible be causing the problem. My engine mechanic has no clue. Honestly, I don't want him near my 4runner anymore!