I am having the exact same problem.
I can host a custom game but when I join one I get booted after the map loads every time.
My upload limit is 0.21 (alot better than LordCarlos).
I did join 3 custom games with no problems then it just stopped working
Still no response from Stardock Support as I guess they are VERY busy making a new patch that will fix all the probs.
Oh and I have followed every peice of advice on the forums so far and even uninstalled Impulse and Demigod completly re-downloaded and reinstalled..... still no joy.
Hopefully a soultion can be found as it seems many people have issues with Demigod.
If I cant get online by the end of the week Stardock can refund my money.
Chocy