I'm not sure of that year, but the truck engines used steel timing gears. Where as the car engines had a phenolic cam gear for quiet operation. They could strip teeth off, especially at high miles, and age. High loading like you did can cause some violent torsional vibration in the crankshaft, and with old damper etc. that could possibly strip teeth or shear a key that locates the gear. Its likely due for an overhaul.
There is no timing chain on 235's.
