2004 jeep liberty help?

i have 2004 jeep liberty with 90,000 miles on fathers day it started to stall and the engine started to shake . the truck has been well maintained i had it put on the computer code P0300 mutiple misfire came up so i brought it to the shop and he said i need a new engine.. thhis doesnt seem right ive only had the truck under a year and have never had an engine go before 100,000 miles any sugesstions thanks