1993 Toyota T-100 5 speed 2 wheel drive

I have a Standard 1993 Toyota T-100 that has been a great pick-up. I have had it since I got it new in April of 1993. it’s been rock solid with the only major repairs being the entire break system. It’s got over 140,000 miles on it so far

As of late when ever I press the clutch inand change gears from 1 through 4 never 4th to 5th I hear a KERTHUNK sound. If I release the clutch very very slowly it doesn’t happen as often, but it still happens once in a while. I can keep it in say 3rd gear and press the clutch in and release it with out changing gears and not get the noise as far as I can hear.

I’m beginning to wonder if this is the U-Joint or possibly a throwout bareing starting to go.

Any ideas or suggestions.

I’m leaning more towards a u-joint. If the throwout bearing were bad, it would squeal like a banshee when you engage the clutch. With this truck, you should be able to slide under and twist the driveshaft by hand. If a u-joint is going bad, you’ll feel play in the driveshaft as you twist it one way and the other.