New starter dragging making grinding noises

Is the starter staying engaged after you release the key? Does the grinding noise continue when the key is released?

Was the old starter doing the same thing?. Check the flywheel, it may be worn

The noise could be because the bendix on starter is hitting on the flywheel after truck is running because the stater is staying on. If you replaced starter and it's doing the same thing, check to see if you have a solenoid relay on the firewall, Positive battery cable goes to it and from there it feeds the starter. If it does have one, disconnect small wire going to it after truck is running, if noise goes away, you have a problem with ignition switch. If noise continues, replace relay