Yes, page load time is a ranking factor. Optimizing pages so they load quickly is listed as a best practice in Google's Webmaster Guidelines. So yes, increased page load load time may decrease rankings. It should definitely decrease traffic. Eight seconds is a looong time these days to wait for a page to load! Have you seen any changes in the SERPs since making these changes?
On the positive side, you must have some fantastic content if users are willing to wait that long for a page to load -- and stay on it for over half an hour I am curious, are you having a lot of repeat traffic?
No, bounce rates do not affect rankings. Matt Cutts has said that if a user visits only one page on a site and finds the information they need, this is a positive user experience. High bounce rates aren't positive for every site, don't get me wrong. If you have an ecommerce site for shoes and you have a very high bounce rate, meaning customers aren't browsing your offerings, writing reviews, and going through checkout, you aren't likely selling very many shoes on the site. The bounce rate is measured in GA to give you the information you need to analyze your site performance in this regard, not for the purpose of ranking your site.
Increased time on page correlates with increased user engagement. Users engage with, and engage longer, with quality content. Or at least highly entertaining content While it is not as clear-cut as to weather this is a ranking factor as is the case for page load time, Google is measuring it and they are all about rewarding websites that provide a great user experience, right?