4hi but no 4lo?

[Ice98]

So for some reason my truck will shift just fine from 2wd to 4hi, and I can feel the difference proving the diff is engaged and the wheels are pulling

but when I try to get it to go from 2wd to 4lo, or even from 4hi to 4lo the button just flashes for 15-20 seconds and then stays in 4hi

Any idea why this would be? Mechanical or Computer problem?

Have no check engine lights, haven't had it coded yet but that may be the next step

 

[Ice98]

So I have been trying to shift going <5mph and apparently I missed the part where it says 1-3mph/neutral (which isn't easy to accomplish) but I did get it to go into 4lo, albeit with a bit of a clunk (its pretty cold here today, maybe in the high 30s/low 40s)

So according to the manual, 4hi/2hi any speed(Not that I am going to switch into 4hi going 60), into or out of 4lo it must be <3mph and preferably in nuetral

 

[lesterl]

Preferrably in park/neutral at 0mph on any of these Style I have ran......