You probably need to readjust your shift rods if you had the shifter out. I assume it is a hurst shifter. If so there is a hole in the side that you put a rod (I use an allen wrench) through and it lines up all the levers on the shifter in neutral. Then making sure the trans is in neutral on the gears, readjust the adjusters to drop back in the holes on the shifter levers.

You probably have it slightly caught between two gears on the shifter---or the trans. With the earlier 833 side covers, this is rather easy to do. Not so much on the later side covers but still possible. Simply removing the shifter rods from the shifter and readjusting everything as above should cure the issue.

One thing I will add is no matter what, when I lined up the levers on my different transmissions I used in my Dart and even with different shifter bodies, I could never insert the allen wrench so it would also go through the reverse lever and have everything work as intended, (luckily thats the last lever in line). So i would just do it to the foward gears and do the reverse seperate and never had an issue. Not sure why it happened, but If I lined up reverse like I was supposed to, I could never get it to go in. So this is the way I do it now. Besides, I am more concerned with foward gears than anything---hate missing a shift due to any mis-alignment.