Complex sentence: This was more of a problem with the 5.3L version than the later 6.0L derivative and affected a small number of vehicles in markets where sustained high-speed driving (well over 120mph) was followed by a period of closed-throttle running.
Split into simpler sentences: This was more of a issue with the 5.3L version than the later 6.0L derivative. In service this was an issue with a small number of vehicles in markets where sustained high-speed driving (well over 120mph) was followed by a period of closed-throttle running.