I recently bought my 1st 4runner, a '98 4wd 3.0 v6. It had a new short block and heads re-worked 4,000 miles ago. Also, the cat was gutted. It has a serious lack of power. My mechanic thinks the timing belt may have slipped a notch - throwing the valve timing off. I don't think the cat would be a problem since the oxygen sensor is upstream. Any thoughts on causes of serious lack of power?