installed dist.trucks running but can't get on timing mark

'IF' you have the distributor installed correctly... The cam retard (distributor adjustment) has got to be set with proper scan tool to 0.. +/- 2° on scanner live data - using functional test....That's how it's done!

Did you unplug the ignition system wire before you set the timing? It is located under the dash, (glovebox) and is black and tan. Unplug, set the timing, shut engine off then replug and it should be fine.