1999 Sierra Transmission issue
 

i need some advice....

my tranny went out in my 1999 gmc sierra, z71 and i purchased a used transmission that is supposed to only have 1000 miles on it. the first couple of days, it felt fine, but now the shift from first to second is extremely rough. i took it and had the transmission flushed and new fluid put in. that did not help. i am worried that something is going foul. it seemed like my old one did the same thing before it went out.

please help.