Cabin smells like burn oil after having the truck serviced

It sounds like they did all the work but the oil coolant and such that spills out when you take the engine apart, even after draining it, is getting hot and burning off. That is likely the smell. It will go away eventually, or you can get a can of spray on engine cleaner and warm up the engine, spray on the cleaner and let it set for a bit, then use a hose to rinse off the cleaner and the mix of crud that is causing the smell. It is likely to be on the exhaust system parts or nearby. Read all warnings and follow any local laws when doing this.