Why not just break into his garage when he wasn't home and steal the damn thing. For that matter, with the sort of mark up you're talking about, why not just buy it flat out and resell it overseas? Lack of money is hardly a prohibitive object in this case.
Their fee's for the theft may have been exactly what the price of the truck was to buy. I could see 20K being a very realistic price in getting the truck from the owners driveway to a shipping container. To the final owner of the truck overseas...to them it makes no difference if it was bought or stolen as they are paying the same price for the truck eventually once it is in there own hands (in most cases the final buyer of the truck would have no idea how it actually got to their country).
Killing TB easily could have been an accident as a struggle happened while trying to kick him out of the vehicle or something else and they had no plans of taking a body back to the farm that night. Also, if you look at that incinerator...it was actually on the small size as that model was built for chickens and small animals which is why it possibly didn't do a complete incineration job on the body where as a larger model for Hogs or Cattle may have. The incinerator he had may just have been the perfect size in the past for getting rid of documents and vehical info just like mentioned in previous posts.