Car overheats!

[CDsDontBurn]

The car:
This is MN12 (1997, 4.6L v8).

The issue:
This happens usually during hotter times of the year like summer. The temp needle just climbs up just a tad below the "H" line in stop-and-go traffic on the highway or on city streets. During normal highway driving w/o any traffic it would go as high as 2/3 of the way up before the "H" line. During winter or any cooler part of the year, the highest to the "H" line the needle gets is about 1/2 way up. So, this is really only a concern on warmer or hot days like now during the summer.

The things done so far:
1. I have replaced the radiator fan as the OEM one had seized up and the blades were no longer moving even by hand.

2. I have replaced the thermostat and O-Ring for an OEM one from the stealership *1.

This seemed to help out the most as now the engine temps stay a little cooler than what they would before.

The unknown:
How do I know if there is any gunk in the cooling system somewhere that is preventing proper coolant flow? I don't see any of the typical orange discoloration of the cooling fluid indicating that it needs to be replaced and the radiator isn't leaking (that would be quite obvious though) either. I have no idea about the water pump and it's condition though nor if it was ever previously replaced or not.

The results thus far
After replacing the thermostat from that cheap-O no-name one from Kragen/O'Reily's with an OEM one and the radiator fan, both seem to have helped out quite a bit. Now the highest to the "H" the needle gets to in stop-and-go-traffic is about 3/4 of the way up on a hot day. On the highway at normal highway speeds, the highest it'll go is about 1/2 of the way up.

The questions:
1. Should I get the current fluid flushed out and replaced even though there is no orange discoloration?

2. How would I know if there are any issues with the water pump? With all of the other cars I've owned and worked on, I have always been able to remove the radiator cap from the radiator itself and just look at the flow of the fluid moving up and down as adequate. With the tbird here, it seems that the overflow tank also doubles as the location to add coolant. And since it's not on the radiator itself, how can I see if the coolant is moving up and down?

3. What are the indications that would tell me that the radiator should be replaced besides a cracked radiator?

*1 - The O-Ring was $15 and thermostat $30 IIRC