The oil tank needs to have a sender integrated into the cap. It will have 2 metal posts for the SmartCraft leads. If you replaced the tank and it doesn’t have the sender or the leads aren’t connected then that would cause it. Just take the sender from the old oil tank.
Speed should take from the GPS anyway, just wire the GPS leads for NMEA-out to the NMEA-in leads on the SmartCraft network. Then configure it in the menus in SmartCraft and the GPS.
Trim and oil level are settings in the SmartCraft setup screens that have to be turned on as well. So if the SmartCraft Speedo was replaced, then the default config was probably used, so I would start with going through the setups on both the Speedo and Tach before doing anything else. The wiring to the oil sender and GPS may all already be done.