49 international H with 2 speed

We are trying to restore, the 5th gear jumps out of gear in high and low. All the rest of the gears work okay. It seems as if the fifth gear don"t fully engage. As soon as you let clutch out it pops out of gear.

It is a common problem, and not terrible, but not easy to fix. It is caused from 60 years of being shifted rather harshly from 4th into fifth grinding a little off of fifth each shift.
The trans is called a 9 speed because that is how many it has. The aftermarket auxiliary gears it has are made by M&W or others. The gear set changes the ratio of the countershaft, allowing it to have 1234 in regular Farmall ratios, then if in high range, H1 H2 H3 H4 these speeds (as I'm shure you know are between 4th and High/road gear.
Fifth is the same in either "range"
Fifth is a direct drive through trans input output shaft and is a sliding set of splines that couple the shafts together (fourth fifth sliding gear is the part that moves.
Repair means getting a good input shaft with great splines,
A new intermediate bearing (also called transmission pilot bearing), and a 4th fifth slider.
The top of the trans (platform must be removed)
The Liftall pump out from the bottom, the clutch shaft and drive coupling removed, and the input bearing/shaft and constant mesh gear. (be careful to not loose intermediate bearing rollers into the trans case, they do come apart).
Driving it as is is no problem, but it is always nice to have high gear. JimN

Unless you have a bearing or shift fork problem you have troubles. The input shaft and 4 to 5 sliding gear is part of the 9 speed parts and harder to find replacement parts. As JN said gear 5 is the same for both ranges.

Also check your shift detent springs while the cover is off.