Perkins 4108 runaway.

[sartorst]

Thank you for returning to update everyone many of these threads end in a mystery because the poster only wants answers and not to help others. Now this thread will be valuable to many

[avazquez]

This one was tricky because in neutral the engine would have normal behavior. In gear, loaded it felt sluggish and without power and wouldn't reach normal rpm's. It could easily end up in major tearing apart looking for the reason.
Some even suggested that the engine could be tired and worn.

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[zeehag]

you are most fortunate yours didnt literally runaway. mine did. was not easy f ix--all had to be rebuilt. excellent save.