I don't know about a diesel, but we owned a 1993 Allegro Bay 27 1/2 foot class C motor home built on a Ford E350 gas chassis. Tiffin built them for several years.
We owned this RV for just about ten years and it never caused any problems mechanically. We lived in Homestead, Fl at the time when the kids were young and the coach delaminated a little on one side and the rubber roof ripped. So, if you are looking for a RV made by Tiffin in that time period, I would think that it would be a basic machine; no slides, no jacks, no fancy electronics and possibly a very good engine and drive chain.
2012 Tiffin Allegro 34 TGA
Ford V-10 22000 lb chassis
Brake Buddy Advantage,