If it's under warrenty I'd take it in....If not I'd make your friend pay to fix it.
in that case....take it to the dealer!I am not familiar with 4 lo in the frontier, though I used 4 lo in my dads f150 on many occasions. I have only used 4 lo once in my truck since I got it and So I don't remember how it drove then, but this just seems wrong.
I mean I know how 4 lo should be where as it doesn't accelerate quickly because it doubles the gearing and all but in detail, i stop, put my truck into neutral, switch into 4 lo. Right after that, i hear the normal clunk but it then the lo doesnt go solid and i hear it clunk a few more times and then itll go solid after a few seconds. Once engaged, i put it back into drive and accelerate and its atleast 3500 rpm before the truck moves and then it immediately shifts and lurches extremely hard (for those who drive stick, is feels like a newbie popping the clutch and the car about dies kinda lurch) and on... And it feels like their is absolutely no pull.