Slant Six Bogging Down!

Having some issues recently with my engine bogging down and eventually dying. It will start up just fine but it seems to be when I am under any sort of load that it will sputter and run very slow. For example I will be on the gas and it will start to sputter until I let my foot off to 10% throttle or less. I ended up going 20mph all the way up a hill with a huge line of traffic following. I have had a misfiring issue that seems to have been getting worse over the past few months, don't know if that would have any effect on my problem. I have changed out the ignition coil, plugs but not wires. Not sure exactly whats wrong (If it is a fuel issue, ignition problem or something else), I have look at other threads but can't seem to find the answer. Any help would be appreciated.