Some start in 1st, some in 2nd, depending on how the factory set them up. If it's a 602 with a 722.4, it's probably first gear start.

It's certainly worth a few minutes to adjust the bowden cable, vacuum modulator, fluid and filter. A viscosity improving additive may help you for awhile. Sometimes you get lucky.

The reason that the 3/4 shift is a problem is that 4th gear requires both clutches to be pressurized, so it places the most stress on the hydraulics. The cause may be wear on the clutch or leaky internal seal, with the clutch pack seals being most common. If you put a gauge on it, I suspect you will find that there's a big pressure drop as you are engaging 4th.