The NP435 and T18 have a "granny gear" first, you do not use it unless you are moving a serious load. Start in second and drive it like you normally would. This is not a shortcut, it is in the owners manual of your truck. The shifter would have been more appropriately marked "L-1-2-3" than the 1 through 4 it has on it.
Aye, that's how I drive most of the time. But again, high-geared heavy truck, 2nd is not always a good choice even when super-low 1st is technically still not needed - but I'll take creeping over slipping the clutch any day. And funny you should mention it, but my shift knob does actually say "L-1-2-3" on it, it's a SM465 shift knob out of a GM truck - I put it on cause to me it just looks and feels better than the Ford mushroom, and like you I also find that pattern more suitable for how the transmission should be driven. Bonus points for being a self-defense weapon in disguise, if someone attacks you all you gotta do is spin the knob off and nail them in the head with it, thing is so ridiculously heavy it pretty much guarantees they won't be getting up any time soon
Direct bolt-on swap if anyone cares, same 3/8" fine thread on both Ford and GM shifters.
Even if your transmission was new and not wore out you would not get a smooth 1-2 shift out of a NP435 (or T18).
Ok, why is that, because of how big the gear ratio jump is, or because 1st is non-sync? Cause I've driven gasser creeper gear ZF5s and they felt pretty smooth, but they are obviously fully synchronized transmissions. So it's just the sliding gear design of the NP435 and T18 that causes the choppy 1-2 shift? Still, a slightly choppy 1-2 is not going to be a deal breaker, as long as transmissions is not quite the fighter she is now kiddo will be happy with her.
Oh, and to answer your question, yes, with the transmission and clutch working properly the NP will shift as smoothly as the T19
So this, together with what everyone else said, means a rebuild would not be a waste of time and effort, and so she will be coming out for that in the near future. During which time she will be temporarily replaced in the line of duty by either another NP435 or a 6.32 T19, waiting on both sellers to get back to me for this.