Memory thrashing

With current main branch (after fixing the build error of not enough arguments for getLowestHash) I noticed that initial blocks sync very fast, but after maybe 20-30 seconds it slows to a crawl. When I hooked up the CPU and memory profiler, it appears to be spending roughly 50 percent of cpu time in garbage collection. Haven't figured out where all the thrashing or leaks are coming from yet, but wanted to raise the issue here for further visibility.