My TBR7 is slipping 5th gear
 

My TBR7 is slipping 5th gear when I shift hard. I’m not sure what’s going on with it. The gear indicator will even stutter when it’s slipping. Any ideas on what the issue can be and how to fix it? Like I said though it only happens when I’m being slightly aggressive when shifting. Thank y’all!!

My Bashan would miss 5th a lot when I first got it. I changed the oil to synthetic and it smoothed right out shortly thereafter. The previous owner had bad oil in it and way too much of it.