Need help 89 f350
 

I just picked up a 89 f350 with the 460 in it and it has issues running once it warms up. It starts sputtering then dies what I've done so far is replaced spark plugs, wires, cap and roter, fuel filter, K&N air filter, water pump (it was leaking), hoses, belts, oil change and oil filter. What may be wrong with it?:confused: Here is some info that may be helpful

Truck has 139k mi sat for last 7 or so years with ocational starts. Has propane system in it and when running propane it runs just time warm or cold. When running gas or propane it smells ritch. I am totally lost

another question when should the truck shift? It's an automatic

Thanks for the help