Any possible way to test an ECU?

Look guys, sorry this isnt about Mustangs but its close, and I have run out of places to go. I need to test out the ECU in my Bronco because I suspect it has gone bad. My transmission has quit shifting on me, and being that the trans is computer operated I think this is the problem. How can I test this out? Id hate to order a replacement ECU and find out this is not the problem.

Its a situation where the trans worked with the old motor in, but not now with the new motor in so its not that. But Ill try calling around tranny shops and see what they say. Thanks for the suggestion. Keep em coming guys.