Actually, you're a little light on memory with just 8 GB. 16 GB would be much better.
And by giving AE so much memory, you may actually be hurting your performance. Try going with 4GB instead of 6.1 gigs.
But you DO need more memory.
I was thinking the same thing, but before I had a workstation laptop with 32G of memory, a worse graphics card and a decent CPU. I was having the same problem, and I allocated around 15-20G and was still having the same problem. I'll try what you said to do.
OK, it seems to be better, your probably right about there not being enough RAM for it to preview a lot of frames. Would faster RAM make a difference along with more GB's
Most RAM is pretty speedy. Faster processors always help.