GM Diesel 3-53 Lacking Power

Purchased a project backhoe with the 3-53 engine and after replacing the battery, primary & secondary fuel filters along with rebuilding the fuel pump, the engine seems to be without a whole lot of power. Has a tachometer on board but inop. Where on a diesel engine should the tachometer be connected to? Any ideas on what could be robbing power?

GM Diesel 3-53 Lacking Power