Deleted member 89374
Sounds like a synchronizer issue. I bet if you rev-matched that gear, it would go in easier. But, I mean, who would want to rev-match 2nd?2nd doesn't grab it just really does not want to let you in unless you pause.
Manual transmissions are way more flexible on the fluid you use. If you want to try an ATF, I would go with Castrol TranSynd TES-668. I run it in three transfer cases that are all different: in a BW44-44 (clutch coupling for front axle) in a RAM 1500, a MP2010 (no clutch, just gears and a planetary differential), and a MP3010 (clutch coupling on demand and low range gears) in the Jeep. They all run perfectly fine with it, and I noticed a reduction in noise when switching modes in the RAM 1500 and the Jeep. It's more "stout", so to speak, than any other ATF out there. And if you don't like how it shifts, drain it out. It's cheap enough that it won't burn a hole in your pocket, yet this stuff is unkillable. There is also Delvac 1 ATF TES-295, but the friction modification is based on a spec that's like 18 years old by now. I'd go with TES-668. Oh, by the way, either of the two TES fluids can be used as a replacement for ATF+ 4, but TES-668 will provide smoother shifts.
I don't put much stock in ZF's recommendations. I mean, I run Mobil 1 LV ATF HP Dexron HP in a 8HP70, so, there is that. I also run Delvac 1 75W-90 in all the diffs, very good gear oil. There is also a Limited Slip version of it, but it's nearly impossible to find. So is Delvac 1 ATF TES-668, but it exists, and it uses GTL as the base oil, as does Dexron HP.