I'm not sure what the newer Rangers run for a tranny, but my pickup has the M5OD in it. I had a very frustrating and similar problem for a while, until it finally gave up the ghost and we solved the problem.
My pickup would be really hard to get into first (from stoplights usually), and when I would go to shift from first to second it would hang really bad as well. The times it wouldn't go into first, it would grind really hard going into reverse. Ended up being a slave cylinder issue in the clutch. After about 6 months it finally failed. We checked everything out before it failed (dad's a 35 yr mechanic and shop owner) and it all looked fine, but finally it just "popped" and that was the end of it.
It's somewhat different in my case though, as I have a 3.0L master cylinder pushing on a 5.0L slave and pressure plate, so my system is under more load than it was intended for. However, it is entirely likely that you have the same problem. Since it finally gave up and we swapped it, my pickup shifts TONS better and it's alot more fun to drive. I love my truck, but when it shifted like sh!t I was getting really really sick of it and not being able to pinpoint the problem, so I hope this helps ya. I sure found it annoying.