Hi yall, I have a 96 Chevy 1500 v8 305 and first thing in the morning it starts up quick first try. But then once i drive it, turn it off and try to start it back up it takes a few tries, with the help of pumping the gas pedal a few times,for it to turn on again. It's like that all day until the next morning. Also when driving over 50 mph and I let off the gas halfway it feels like it misfires and yesterday I got a p0420 so I swapped 02 sensors but no change. The hard starts I noticed shortly after replacing ecm Not sure if any of this is related but any info would help. Thanks

 

Oh yea it also smells like its running rich at start up

 

when was the last tune-up? backfires are usually caused by leaking exhaust, with it running get under the truck and feel for leaks there ia an o2 sensor after the cat too

 

Last tune up was done 3 months ago changed spark plugs and wires fuel filter air filter cap and rotor belt coolant flush pcv valve I checked for leaks in pipes but nothing noticeable. My scan tool brought up code p0420 which is something to do with the cats do you think that might have something to do wi
th it