Hello could really use some help,

I went to Aamco to check the transmission in my 1990 jeep cherokee laredo 4x4 - 4.0 6 cyl. The issue was No engine braking in 3rd an no manual 1-2 shift. My girlfriend used 4x4 and it apparently made some loud cracks and hasn't work since, and I have not tried to use it sense plus I was not there to hear it break.

Should I drop them both and inspect? I have also found a transmission with from an 89 that has 75k on it.