I have a 2005 Silverado 4by4 with the v-6 . The motor has 217,000 miles on it. It's been dependable, but not very powerful. I was wondering if the motor ever went bad, could a v-8 be put in it .

It can be done but you would need a donor truck to swap all of the components and tennis shoes is right, it's a very involved process.

get a junk yard complete set up including radiator and ecm including the harness they sell kits, you must know what your doing otherwise buy a new truck