2000 ram burns to ground after crank replacement.........

2000 dodge ram 1500 quod cab sport . I bout this truck at us auto sails in gainsville ga... I drove it for 3 months and the engine started knocking really loud. thay refused to even talk about it. so still under warranty I pulled the motor out put a crank shaft and barring's with front and main seals in it than after almost loosing my job do to this for the 3 days I was out I finally got it running than 2 weeks later it burns to the ground. where did I go wrong