Buying used: need advice (4x4 related)

You can be in any gear to engage 4hi/2hi. Stopped and in Neutral to switch to 4lo

 

In gs no problem it will go in in a variety af circumstances but this 12y 4x taco owner will tell u in my experience ( YMMV) is that going from 2x to 4x is smooth, fast, clunk free, at low speeds with steering wheel straight, off gas, going down a gentle slope, but that part isn't that important, I shift into 4 going up hill 90%?of the time. Hope helps !!!!!&!!!!!!?
My technique.... 10/ 20 mph. slo/ let off gas, but w still enuf momentum to carry the taco for 30+ ft ..... still stay light on the gas.... Straighen steering. ( do this before the letting off of the gas) Flip switch to 4wd. Lil pulse gas then gas off, if it doesn't drop in rite away.
That said few trails are straight with a straight, downhill grade when u need yer 4wd. So slowdown , try a few of the things above. It will go in at some point. ... it's been working for mine and has the least of the thunk and thuds involved in going into 4x

 

Good advice listed here.