If you manually try to unlock the other doors, do the mechanisms move freely or is there a good degree of resistance?
If they're difficult to move, the actuator rods need cleaning and re-lubing where they go through the plastic slider clip on the inner door panel. This is a fairly common issue once these trucks get older and it's very easy to fix. Remove the door panel and then operate the manual lock knob so you see which rod it uses (there are two - other is for the interior door handle) then gently pry it out of the white plastic clip you see about midway down. A little brake parts cleaner on a paper towel to wipe off the old grease, then apply a little fresh lithium grease to that area of the rod and pop it back in - work it a few times to spread the grease in the slider. Repeat to the other doors as well.
I've had them gum up the old lube so bad I just about broke the key off in the lock. The momentary pulse the keyless entry unit sends out to unlock the doors is no match for that.
Richard