Could be an air bubble you introduced whilst popping the cap. Never a good idea, you know that now...
But yes, that's kinda putting a lot of restriction in front of the radiator there. The heat from the transmission oil is being transferred to the air passing through the coolers, and then that air can't pick up any more heat from the radiator. I noticed my temps come up to normal quicker after I added a massive trans oil cooler, but I don't think 220-225 is anything to worry about, really. Normal is normal. However, 250 is starting to trip off alarm bells in my head!
I think you should remove that extra trans cooler and try to burp the cooling system of any air bubbles. Oh, while you're at it, get a mix of 50/50 in there so the metals are protected and you have more boil-over protection.