1951 F4 loses power in 4th gear?

[scooder]

Welcome to the Barn, I really like your truck, beautiful.
I agree with above, especially the question regarding your loss of power, is the engine dying or revs climbing but truck not going faster?
Don't recall if there synchronised four speeds in your truck?
Mac Vanpelt clutch test, start the engine, put your hoof on the clutch, count slowly to twenty, try to engage first gear. If you get a grind, the clutch ain't releasing properly, could be adjustment (1 - 1 1/2" free play at the pedal depending on information source) or contaminated clutch disc requiring replacement.
Measure your pedal free play. And let us know.
Martin.