Car getting real hot....

Ok experts

Here is my dilemma and up here we don't have that many great mopar experts.
I will try to tell you everything you need to know about the problem.

Rebuilt 340 six pack, less than 1500 miles, rebuilt last yr, before that I never had heating issues.
I don't know now if it's the guage but I do feel the car a little hotter than before.
When I'm driving on the highway non stop the car will reach 160 and stay there but if I start to get stuck in traffic it goes up real fast, if I shut your car off (160) it will go to 180 and higher but when I start moving it will come down a little bit 10 mins bumper traffic it can reach closer 190. 200 it had not overheated ever but I haven't allowed it also as I shut it off.
If I start to drive just in the city within 10 15 mins @ 25-30 degrees (77 - 86 Fahrenheit) it starts to get hot to 180 and climbing to 200 soon after.

The rad. Is an after market (Bcool I think,) nice rad I never had these problem before. We changed the thermostat (i think it's a 180, not sure) I have water and antifreeze. It's a 4 speed with 4.10 rear gears.
The engine is basically. stock aside from a cam (550 lift) solid lifter as well like the cam.
The shroud I have is very thin came with the rad and like I said I never had these problems, I changed the water temp guage with the rebuilt engine so I'm really confused.
Is it a water pump, the guage, I changed the belt also.
May be the cap I've been told,
Any thoughts? You are the only people that I truly trust with A body mopars... Then I go to the shop and tell them do so and so... So any help will be appreciated.
Regards,
MAPS
No rare at all for a "rebuilt" engine to run a little hotter.
Not abnormal for engines to get hot after they are shut off, it is called
"heat soaking"
Your worst enemy is the 4.10 gear you are running.
With 50/50 coolant the system will not boil over unit 230-240*F
Drive it