Solenoid block or Servo pin bore?

[Explorer&Popup]

My '02 Explorer 4.0L trans is running RPM's up to 3500-4000 then after it slips and drops the RPM's back down it shifts to 3rd causing the o/d indicator to flash rapidly. I do not have a code reader. So best guess from all I have read is one of two things.
1. Servo pin bore is worn and the cheapest option would be o-rings.
2. Refurbished Solenoid Block Pack.
Thoughts and suggestions would be greatly appreciated.

 

[BrooklynBay]

Welcome to this forum! Don't guess what the issue is when you could have a shop scan it. This is why there's a code present. It tells you what is going on inside the transmission.