...,new mtr $3000. used mtr $1500? replaced heads on motor about 3mnths ago, now have a rod knocing and metel in the oil pan.. $3000 for new motor , or $1500 for a used. the new one has a 3yr 100,000 mile warry. the used has no warry. the truck is paid for, but probally only worth about $6000, just worried if i spend all this money the tranny is next, any advice.. truck has 153,000 miles now..