Hey there, have a 2005 Chevy Suburban 1500 LT 4x2 flex fuel with 202k miles on it.

lately been having issues starting the truck up after doing some work on it. Before it would startup no problem and runs smooth still but now it won’t start on the first crank but will on the second one.

Like I said i did some work on it before the issue started. I removed the intake manifold as well as released fuel pressure before doing so. In order to replace the oil pressure sensor, cam shaft position sensor, and air intake manifold gaskets. Then since I had the manifold off I replaced the ignition coils and wires. Not the spark plugs because those are fairly new still. Also replaced canister purge valve.

after putting it back together I noticed right away the issue when starting it back up. Tried a few times and then drove it for a good while and the issue persisted.

I bought more parts to change however I had a mechanic do the work and take a look into the startup issue. I had the vapor canister, vapor canister vent solenoid, fuel pump, replaced regarding the fuel system. When done the mechanic said it will take a few days of driving for the computer to reset itself to fix the issue completely. Also had the steering wheel position sensor replaced. 

so, what do I do? Was the mechanic right? I saw videos that maybe I still need to replace the fuel filter since my old man never changed it once. Also that there can be issue with the PCV valve. Could it be an issue with the throttle body? But other than that I don’t know what else to check.