You are on the right track. Double check the belt timing. Also another thing to consider is the cam chain and tensioner. Sometimes the cam tensioner will wear down or become weak causing the cams to be off slightly on acceleration. There is a plastic foot on the tensioner. This is usually caused by low oil pressure caused by lack of oil changes and sludge issues . This may not be the issure but something to consider. Also the cam sensor could be faulty.