Large files and multiple if statement Issues in Python

I am having speed issues using multiple "if/elif statements" when trying to read through and print a large file. When timing my code it took almost 10 mins to read through and replace 2MB file lol. The sample file I used had roughly 8 characters on a line. Example (ABAABAA, AAAAA, BAABABAB)

with open("text2.txt","r") as File1:
        for line in File1:
                    W = 'A'
                    Z = 'B'
                    counting1 = line.count(W)
                    counting2 = line.count(Z)
                    if counting1 == 1:
                        removeW = line.replace(W,'C')
                        removeZ = line.replace(Z,'D')
                        print (removeW)
                        print (removeZ)
                        if counting2 == 2:
                            removeW = line.replace(W,'E')
                            removeZ = line.replace(Z,'F')
                            print (removeW)
                            print (removeZ)
                    elif counting1 == 2:
                        removeW = line.replace(W,'G')
                        removeZ = line.replace(Z,'H')
                        if counting2 == 3:
                            removeW = line.replace(W,'E')
                            removeZ = line.replace(Z,'F')
                            print (removeW)
                            print (removeZ)
                    elif counting1 == 3:
                        removeW = line.replace(W,'I')
                        removeZ = line.replace(Z,'J')
                        print (removeW)
                        print (removeZ)

I have a decent computer, because I'm so new at coding can someone assist me with cleaning that up and/or teach me just a better process for speed purposes. I have 2 nested if statements and because of the different possibilities not sure a better way.