By far one of the cheapest upgrades you can do to increase the reliability of your modified 6.4 Powerstroke.
With higher rpm's, higher boost level,s or higher backpressure levels, the factory pushrods can begin to flex and/or bend.
With a bent pushrod, valve lift can be limited, resulting in low compression, lost power, or even a miss.
Pushrods are stock diameter, so no modification is required on the headgasket, but are strong enough to withstand any abuse you can throw at them. This makes them a true drop in upgrade that you can do yourself.