Saying "it smokes" is pretty subjective. Some smoke would be normal when cold, and smoke when we blew our turbo was just incredible - leading people that saw it to call the fire department.
My point is you should have it looked at by somebody that knows what's going on. Many states require an annual safety inspection on the bigger trucks. Facilities that do those generally charge a very reasonable fee for that inspection (200-250.). That fee would put a pro's eyes on your issue, and I'm sure they'd be willing to give their opinion at that point. To be sure, often diagnostics will need to be run, and I'm pretty sure that will be on your dime.
Without that expert opinion on the "smoke", I'd pass.
1997 37' HR Endeavor, 275hp Cat, Freightliner
03 CR-V Blue Ox, Ready Brake