I have an 86 N/a Manual that I’ve had for about three years now runs good(not great) only done small upgrades aluminum radiator cold air intake. Recently I’ve been hearing this god awful clunking when I shift thinking it was the clutch(cause I just replaced the slave cylinder and master cylinder) I replaced the clutch and fly wheel. Still hearing the noise after the replacement of all these parts. Noticed it only clunks when I put my foot on the gas and take my foot off the gas. It it doesn’t always make the noise I have no clue what it could be thank you for your time sorry for my limited knowledge

motor mounts?

i would check the cv joints

I'm guessing the differential.

Go down the road around 25mph in 3rd gear. LIGHTLY tap the throttle, then let off. If it clunks on application and release, that's typically gear lash in the differential.

Next step is to get it up in the air on 4 stands (or a lift). Put it in neutral and rotate the driveshaft. Look for the clunk. May also be U-joints or CV joints, but you should be able to isolate it by rotating the driveshaft.