2003 lance 1171 and 2017 Srw f350 am I asking for trouble?

What Jaycocreek said!
Throwing the blatantly irresponsible aside (like an 1171 on a half ton), a person's knowledge, abilities and comfort level come into play as much as the OE ratings.
OEMs are required to tailor to the least common denominator for liability reasons. Think "don't use in shower" stickers on hair dryers and the "you'll cut your hand off" stickers on lawn mowers.
For someone with limited knowledge, they will generally be safe staying within mfgs published ratings.