p0300 misfire on 2004 express 4.8l 140k. Tried about everything. Any suggestions

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2004 Express van 4.8l with 140k miles. Past couple years: Hard to start after fuel fill up. Random miss and hesitation when accelerating. Pumping throttle would cure. Then randomly again from 30 min to 7 days between. Lately: Missing most of the time, especially when hot. Rough idle and evident miss, no power. Diagnosis so far: Throwing P0300 (random misfire) and p0455 (large EVAP leak) Started with EVAP solenoid at fule tank. Nope. Purge valve solenoid at throttle body. On first start nope. Let cool and ran excellent. Smooth idle, rev fast, plenty of power. Lasted about 20-30 miles. Bad again. Codes Reset. Next plugs and wires. Nope. Removed catalytic converters. Nope Took to shop for scan tool. Shows p0300 (random misfire) and p0175 (bank 2 rich). Also shows misfire history. Cyl 2 and 8 around 3000. Cyl 6 33000! The rest are small numbers. Tested spark at all cyl. Good. Tested cyl 6 without plug wire feels the same. All other make it run worse. Seems like it is #6. Tested #6 compression. 150psi. Back to shop for fuel injector testing (not sure of actual procedure used there to test). They tried MAF and MAP sensors. Nope. They think ECM. To Local Chevy dealer for ECM check. Say its good. Want $200 to diagnose. Their verdict is cam and lifters... I have a hard time with cam and lifters. It will run great at times. Used to be run great all the time and random rare miss. Now the opposite. Miss mostly and run great rarely. Does seem to be best when cold. I am thinking about swaping the 4 and 6 injectors to verify those. Trying to round up a node to test with. Any suggestions before a motor rebuild?