1987 Cadillac Brougham oil consumption

I've had it tuned, new compressor and all the plugs wires, belts replaced. It doesn't smoke at all, doesn't leak oil. Had the oil switch and oil pan bolts tightened.It seemed the oil was coming out a little around the timing chain. Never had a wet/dry test. One of the 3 mechanics said the engine could need a rebuild. His brother said the valves and rings are good but it SUCKS down a quart/oil every three days(180 miles). Do I need to open her up on interstate? It drives great except I feel it doesn't like to go past 50 even tho' it will. I,ve sunk 1200 buckaroos. It was driven by a little old lady and was garage kept for 5 years before I stupidly bought it.