getting all of the air out is certainly a challenge. I have had the same struggles.
I have:
FR radiator
FR trans cooler
SPD 170 Degree Tstat.
With an ambient of 105 degrees, The truck will idle with A/C on at full blast at 180 degrees. On the highway, Cruising at 70-80, my temps are generally about 205. The temps only climb when I'm doing over 100 mph for more than 5-10 minutes. In those cases, the temp will float to 215-220.
Driving hard offroad, between 40 and 80, my temps will float between 205-218.
I had everything but the SPD tstat on my previous trip. My temps went as high as 265.
I'm planning to install some high CFM spal fans to help with cooling at the "middle speeds" but that is me wanting to make the change, not having to make the change.
as for wintertime starts, the Tstat is mechanical and won't open until 170 degrees, so it isn't going to make it take longer to warm up, it will just run cooler.
the bigger radiator won't lower temps, but it will make sure that they do not "swing" wildly. essentially the bigger rad will prevent overheating conditions ) to a degree) and will give you a larger buffer to react and let the truck cool down. The more consistent temps will also prevent the PCM from pulling timing.
as far as air in the system, do you have an aftermarket overflow tank? If so, go back to the stocker. Also, check the plastic fittings for "drip" leaks. I found one on the lower overflow tank line during the last trip, it was allowing a super small leak, but also was allowing air to be reintroduced into the system. It took a while to find it and it was making me think that I had a head or headgasket issue. Nope! just a stupid fitting leak that was fixed with some waterweld.