I know I don't have a Tiffin, but a lot of the components are the same. Each slide has a motor, each motor has a motor controller. Find the controllers and see if there is 12V being applied to them. Two of my controllers got there power from one 12V relay that failed. There are a lot of these little 12V relays used allover the coach, just pull one from somewhere else and try it. I pulled one from an awning circuit, the slides then worked fine.
2019 Fleetwood Discovery LXE 40M w/2021 Equinox