That's not good.
Sounds like you have a blockage in the vacuum system or the micro filter in the tank is bunged up with rubbish. Try revving it up and put a cloth into the vac inlet and see if it arrives in the tank or gets stuck, probably where the suction line joins the tank. Failing that you've got a faulty vac gauge.
A blockage would certainly explain the overheating issue but with it you would have higher than normal fuel consumption as the engine is working harder than normal to fight the restriction in the suction system and hence overheating which really isn't good.
Simon