130 gpm cooling upgrade explained

While troubleshooting my high idle problem, I happened along another cooling issue. I say another because the two might be related.
It seems my engine is not reaching normal operating temperature, which before I replaced the OEM 87 gpm system, was about 180 degrees F. According to dash gauge and an external thermometer, coolant is only reaching about 145 degrees F. It doesn't matter if it is just idling or after driving for 30 minutes or more, same temp about 145 degrees F. I tried burbing air from system, which air bubbles did come out, but no change. Also, I can touch top rad hose which is hot but not so hot you have to let go. Bottom rad hose is just barely warm, and probably not from coolant warming it.
Again, I did not perform the install but now I hesitate on letting to shop troubleshoot this issue, lack of trust at this point.
Can anyone explain how this dual T-stat cooling system actually works so I'll have a better idea where to go with this issue. To me, this thing is acting like the T-stats where never even installed. I know it's hard to imagine but you never know.

Have you looked to see if there are stats in it?

Only use AC Delco brand stats, others are known to not work as needed...

I had an issue with MR Gasket brand stats. In cold weather my engine would run 160-ish. When I contacted the company, they admitted that they had some issues with a few batches of thermostats. Also, if you are using stats with bypass holes you may experience the same issue.

If the engine temp can't get above 145 and the lower rad hose is warm... it's due to bad/incorrectly installed t-stats.

You can test t-stats in a pan of boiling water and a cooking thermometer. Simple to check them. Jim