Instead of backing the truck up why not put the furniture movers under the table while its facing up in the air, that way you can just wheel it to the truck and have less of a chance of a 400 lb table crushing down on your truck, then you could put a towel or something in the truck bed so it just slides in easier
5 year too late comment response but as a person that moves heavy antique stuff uhh The truck is made for that type of weight and more, had he slid 400lb even further than necessary, he would have been more exhausted when lifting, increasing his risk of being injured and dropping the table, Most Americans cant even push 60 pounds on sliders especially while on cement/concrete
You should modify some type of engine hoist thingy with a winch. I don’t know. I’m not an engineer but it sounds like you could benefit from a massive engine hoist