why would truck start once after changing starter but not again

Recheck your work, loose connection. Bad battery cables is the most common failure but you could also have a bad new starter, just cause it’s new doesn’t mean it’s any good, ignition switch, clutch or park switch.

Make sure batt terminals are tight, .Junk starter ? ? Check fuses / mega fuses / fusible links/relays , See if the solenoid is getting juice when you hit the key .something else may have gone wrong by pure coincidence .