it was not an engine change
The 757-200 suffered "limitations" above 250,000lb TOW; the 757-300 which sold like pork sausages in a synagogue the day before Yom Kippur would have required a modest upgrade in engine rating to 42250lb-st (from 41000) to retain the same TOW/ST rating as the ostensibly replaced 727-200. But it did not happen. Meantime Northwest was a firm P&W lover and went as far as I know to be the only P&W buyer. At less thrust than the roller. The airline I then worked for would not look at a fuselage barrel that was 707/727/757 with a completely different wing to the 767 with no structural strength to go to thrustfuller engines. Yup I know the 757/767 have a common type rating. Nope I don't think the 757 was a good move apart from folks who lived in Renton. Yup I think the 737-900ER is a bag of prawns. Nope I do not work for company "A" any more. Yup I work for company "B". Nope I don't regret. But yup I remember it was difficult times and if I recall engine makers and air-framers were not exactly philanthropic enterprises. And nope, nobody buys my book. And yup I must stop talking like this and go in and have dinner with my family. But what I remember about the 767 is a) appalling number of gotchas but b) she flew rather sweetly for all that. Oh to be young again.