Hi there, i have a 2000 Nu 6 cyl Fairlane, i'm having massive fuel consumption issues, as well as it running rough at idle and spewing black smoke, i noticed it was taking forever to reach temp so i checked the thermostat and found it to be stuck open so i replaced that and did a full flush at the same time (don't know when the last one was done so i figured why not) but it's still using a fair amount of fuel and running like crap at idle what direction should i go down next i was thinking MAPS but i thought id get a few peoples opinions first thank you

Sounds like fuel injectors are dumping way too much fuel in.
Service your injectors or swap the fuel rail / injectors with other.

Check / clean the fuel pressure regulator on the fuel rail. If it's blocked / clogged, the fuel pressure in the rail goes up.

Check for intake blockages, collapsed air filter? That'll make it run rich.

Rough idle may also be a vacuum leak, making the engine run lean, but you have the exact opposite issue...

Black smoke is burnt fuel,
grey, blue smoke is burnt oil.
White smoke is usually heavy condensation, burnt coolant.