I just got a 87 5 speed and it runs fine but if you are in first it bogs till about 15 20 km then it’s fine it’s like you start it in second but I see have all gears the guy before just did a clutch job at a shop and it also likes to kick you out of 3rd 4th and 5th

Dont know about the first gear issue but the jumping out of 3,4 and 5 is probably bad synco rings. Have you checked the fluid level? There is a shop in Minnesota that specializes in Nissan transmissions. Midwest Transmission. They arrange shipping pickup for you and the price includes shipping both ways. They did a great job on my 1981 280zx 5 speed. Or find a used one.