Multi issue questions

I've got a 1996 Chevy C2500 w/ 5.0 Vortec and a 4l60e trans. It has 286,000 miles on it and has been serviced extensively. Started out as a fleet vehicle, so I have all the service records for every nut, bolt and washer that has been installed or replaced since day 1.

My first issue is that somedays it will start right up fine and others it just won't start at all. When it does start and run, it runs absolutely beautiful, no misfiring, sputtering or hesitations at all. It had a new fuel pump, strainer and filter installed at 230k. At 248k a new ignition coil was installed and at 260k a new distributor cap and rotor were put on. This issue seems to have started after I changed the fuel filter. As a test, I changed the filter again. Same issue. Could it be a coincidence that it started just at the same time as changing the filter or is there a really good chance that I bought 2 bad filters? Anyone have any ideas as to where I should start looking first? When I hook up my code reader, the only code that comes up is a 420 which as we know is the EGR valve.

Which brings me to my next issue: EGR valve, replace it or clean it? Anyone on this one? What's the best method for cleaning it? What do I need for supplies before I start?

Now for the final issue, after the motor and trans have warmed up, the truck has a very hard shift from 1st to 2nd gear. After that, it shifts very smoothly into 3rd & 4th. It had a fluid and filter change 276k. It was previously doing the same thing before the service. Any ideas on this one?

I'd like to thank everyone for their time and patience and I welcome any and all suggestions and ideas. Thank you, Charles

On the hard start cold.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold and fuel pressure testing guide line.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

For the question about the EGR, I will tell you my experience.
My 95 K2500 with 67,000 miles ran like a top. I drove it 1600 miles, half with about 600 lbs in the box the other half empty.
Just before I arrived at my destination the engine started running rough and then even started knocking. When I got home I took it to my mechanic and he just looked at the motor and asked me if I just came back from a long trip. I told him I had. He told me that the EGR was bad and it probably burned the valves on the two center cylinders on the right bank. He did a compression check and sure enough they had low compression and I had to have a valve job.
Save yourself some money and get a new EGR before more serious problems.
He could tell that the EGR was bad because the exhaust manifold had turned blue due to excessive heat.