Silverado 98 PCM without cylinders 3 and 4 signal

Greetings everyone, I'm an automotive electronic control module repair technician and I'm starting my own business in this field. My question is: I have a 1998 Silverado automatic in my shop that has a very strange problem. The PCM stops sending the activation signal to injectors 3 and 4 and accelerates the pulse for the injector in cylinder 6, but this problem only occurs in the morning. I've already replaced the respective transistors, including their microcontrollers, and the problem persists. I've also tried another PCM and the same issue remains. What's most curious is that two trucks have had the same problem this week. Could someone please, with all due respect, guide me on how to resolve this issue? I would be very grateful.

If the problem persists with two computers, then it's clear the computer isn't the issue. It could be a faulty sensor, either temperature or position, that's disrupting the PCM parameters.

Thanks for your suggestions and interest in helping me, Kikemec. It was indeed the camshaft position sensor (inside the distributor) that was causing that annoying problem. I hope this information helps anyone else experiencing the same issue. Cheers.