so i replaced my LS transmission to a CTR w/ LSD, i know it works fine because it came from my other car. Which was fine when i took it off. For some reason i can't reverse. I can shift it into (reverse) gear but if i try to accelerate it'll go forward...

Shifter is loose, i mean really loose.. Didnt use the "bitch pin" to connect shift to trans. Didn't have one laying around. Used a bolt and 2 nuts instead. Im guessing that may be the reason why it is loose. Unless i installed something backwards..

help is appreciated.

 

Try disconnecting the shift linkage and test shifting it right at the transmission. This will show you if it is internal or a linkage issue.

 

Sounds like you are selecting 4th and not Reverse. Is there an audible 'click'?

Pull the shift linkage off to fix your linkage to trans issue (no spread pin). You need the correct diameter bolt/pin to go through there or it will have slop and not rotate on the lateral, neutral axis enough to select the left and right shift gates. While you have the shift linkage disconnected, do as Synchrotech says and test shift the transmission without the linkage and make sure it can select Reverse (from behind the transmission, rotating shift rod clockwise, and pushing forward).