Program becomes slow

I have the same problem, it will be chugging along just fine, but then suddenly I'll make a change that upsets it somehow and it'll start playing back jerky. The only solution I've found is to save and quit out of the program and restart it again. This works, but it's very frustrating, especially when you're working on an intricate or difficult section of the video.

WMM isn't up to quality anymore so I was trying this one out because it can actually play my video files. But that's the only thing it has going for it so far. It is so incredibly slow, I cannot do anything. The red time place marker refuses to move or jumps around to someplace it wants to go instead if you (or I?) try to move it. It's alt functions also hardly ever work, and I've been trying to press it nonstop!
When I create videos, I want to keep seeing it from top to bottom so that I can fix any transition issues or out-of-tunement I don't like as it happens. But with this program, it is impossible... because it just doesn't want to do anything and just leaves you hanging. It doesn't even let you press play when you're actually on the scene you want, finally...
So then I still have to fight just trying to get the damn play button to work, and then once it does play, the scenes get played back choppy or glitched up, or it doesn't even play the right scene (in fact... it doesn't even play a scene that's even in the timeline).

If it thinks it's going to take my money with this sort of crappy service it's sadly mistaken. :/