I have a 2006 Pleasure-way Lexor TD on a Chev 3500 chassis ( the chassis is a 2005- which is common with class B's- a chassis a year oldr than the RV...) 6.0L gas
my rated capacity is 5000# w 500# tongue weight.
when I was shopping it seemed that was common rating for this chassis.
I think the Roadtrek 190 models on a Chev 3500 had same rating
If you decide on a class B the big advantages are ease of driving. park anywhere and great mpg- the drawbacks are a high $ per cubic foot of space- a larger RV may actually cost less than a class B!
figure out priorities, ours was bed size- we got the largest we could find, a fore/aft sleeper 72 w x 75L ( a sideways sleeper model will probably top out at 72" long unless a widebody conversion) others who are ok with a smaller bed will have more interior lay out options... I know those who have 72 x 48 and are happy with that- it gves space for a wet bath
Mike