Mine did this after the install. Had one guy build the trans and another shop install it. After an initial drive, within the 1st 5 miles or so, mine did the same thing. I took it back to the installer, and he said the governor part on the outside that regulates the shifts based on its speed could have the weights stuck. Was not the case.
I took it back to my builder who then adjusted the cable a bit more and it ran fine ever since. Sometimes it seems like a harder shift in 2nd when it’s not warmed up yet Or I just don’t drive it enough. It has also been said that after a rebuild, the trans can get stuck in 1st due to debris in the line that wasn’t cleared out yet. Some guys say to stomp on it as few times to see if that’s the case, and it could clear out on its own.
Mine is a hydraulic shift setup with an 87 trans. 4th gear shift timing still needs adjusted bc it waits till 70-75 to shift at 3000 rpms (I think), have a wide band set for 4th. I have 35” tires and a 3.71 gear set based on my “turns”. I’m assuming the governor weight for 4th gear needs to be lighter but I’m not an expert in this sort of thing. I was waiting to take it up to the builder to adjust this but if I can do this on my own someone chime in or reach me offline @fozzieswheels
