Engine now starts and runs at high RPM's

I have removed and reinstalled head in order to replace two broken rocker arms, the engine now starts and runs at high rpm's only (3000 to 40000), hard to tell if it is smooth at these rpm's. My question is would the engine run like this, or at all, if during reassembly the timing chain got a tooth off? I have tried disconnecting the electronic components to the fuel system one by one, the rpm's remain the same, it simply will not idle down. The timing chain is a simple single chain from crank to cam, the engines a straight 6 SOHC. It is a lot of work to check the timing chain marks if that is not the problem, would like suggestions or another simpler cure, a second opinion. Thanks