Yes, sure sounds like a Vacuum Issue. There a few locations where Vacuum Lines connect to the Manifold. Make sure these are all plugged or connected to the proper Lines. Did you replace the Manifold Gasket? If so is it the correct one.
Does the engine have even compression in all cylinders? Is the timing correct?
Just some starting point thoughts

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80 280TE, 5 speed
83 280TE- 5 spd, 16.5mm rear sway
85 280SL- 15" Bundts