My 1999 V6 auto trans f150 has 200000 miles on it .
So far no real bad luck.
I want a V8 can it be done ?

 

it could be done but not easily. You are better off selling your truck and buying one with a v8. Be easier and cheaper to do.

 

what makes it such a hard thing to do ?

 

you'll have to changes transmisions, motors, cooling system, possible a/c and power steering stuff, ECM, wiring harnesses, maybe the dash guages, drive shaft and stuff like that

like gotts said it'll be easier, faster and cheaper to start with a V-8 truck