ok so I have a 95 Blazer trans went out and changed filter drained (not flushed) the trans and she ran great for about a week I was pulling utility trailer no problem got home went to back in no reverse .like 2nd neutral. checked linkage. still nothing I been towing trailer and still driving it with no reverse for 4 months now. any clues how to get reverse back.

 

More than likely you have a broken or stripped reaction/sun shell. Very common in these transmissions. The transmission has to come out and taken apart to replace part. But after driving that amount of time you will find more parts damaged from only running in 1st and 3rd gears plus all the debris created from failed part. Good luck

 

I hate to say it, but it sounds like a rebuild or complete replacement is in your future.