Welcome! Good looking bus! I also have a 2007 Collins built on a Chevy express chassis. Mine has the LMM Duramax diesel in it and I've been having problems with it. Chassis is good and mine drives good! I've been working on sealing some leaky windows up after hard rains.
Just getting started on short bus build...
2007 Collins (Chevy Express 3500)
LMM Duramax Diesel 4L85E Transmission