EVAP system Engine light started flashing?

Long time battle. Engine light for awhile and then started flashing months ago and code came up for purge solenoid valve which I changed. Truck was not getting past 4000rpm in park and would hang at 45 with no acceleration. Checked for water in fuel and was ok. Changed fuel filter anyway. No help.I did have a cat, evap and O2 sensor fault which I put a fuel additive in the engine with high test gas. Light reset and did not come back. Still no acceleration past 45 mph. Exhaust has a smell. Went to do my weekly run around the block and engine started missing violently with the check light and now code po300. Reset everything and erased code. Ran it again with bad missing at idle and engine light came back on with po303 which is cylinder 3 misfire. I'm wondering if the evap system caused excessive fuel to the engine. Also I cannot fuel truck without the pump clicking off immediately. What can I do to check the evap system. The fuel pressure meter back then was about 60psi which appears good. Someone said to check for blocked vent valve at fuel canister. I am providing a picture of that area with hoses. Should I disconnect some and check for a blockage. If so which ones. Im totally lost with chevy crap. Thanks Bob