Question about wheelbase and handling issues???

Apples to basketballs.

Your old one was a gasser on an old, outdated chassis. The Monaco is a diesel pusher with and air ride suspension. Two totally different animals.

Going from memory here, which isn't always good, check for any recalls and/or updates on the rear suspension arms. I can't remember which Monaco chassis had the issue, be sure you do. Not a huge deal but something to be aware of.