When I first started ACAD MEP, I had a new machine that constantly crashed. I found out the video card was not tested by Autodesk. I ugraded the machine for a more robust card which fixed the problem. Most of those who work MEP that I know, HVAC, Plumbing..., have a hard time with performance. I think it's the nature of the program. That said, check your work flow to isolate the objects you're editing. By machine, I mean the total package, RAM, processor, video card, just check to make sure it can handle what you're trying to do.