Should I quit my job before or after going to orientation?

Some companies, especially flatbed or tanker companies, are a bit more strict than others about fitness and the ability to do a bit of hard work.

If you have no serious chronic health issues and can climb one flight of stairs without falling down or sounding like a steam engine, you should be fine.

If you go watch the drivers entering and leaving the fuel islands at a large truck stop for a few hours, you will rapidly see that physical fitness is not particularly important to most companies.

 

You don't yet have a CDL to get a "dime a dozen" driving job nor do you know for sure that driving or OTR work for you since you have no experience.

 

Which is why I said changing careers is a bit different than quitting.

 

The OP is changing careers.