well its never happened to me till now

I have this happen all the time in my line of work. If the truck is a good deal the best thing next to replacing the interior is to give it a thorough cleaning, have a carpet company do full extractions on the seats and carpet and rent an Ozone machine and let it run in the interior with the windows rolled up for a good week.

The smell of a dead body is tough one to get rid of... both in the truck and in your mind.