That is kinda strange I think... If you are running say 50 mph and suddenly come up on snow or something you would think that if you hit 4hi that sudden impact on the front componets would be hard on everything... I know the front tires are moving as fast as the rear tires, but the front axle ect just suddenly locking in would be hard on everything?

 

What is "suddenly locking in"? What is experiencing "sudden impact"? The only time there will be a speed difference of any significant kind in the axle engagement mechanism outside of actual tires slipping is when you are turning sharp (i.e. parking lot type stuff). When was the last time you were going through a parking lot at 50mph? If you are driving straight down the road or through curves where the speed limit is >=50mph and all 4 wheels are going relatively the same speed, 4wd engagement will work pretty much like it would at slow speed. It's all about relative speed difference between the differential stub shaft and the passenger side extension shaft.

But I digress, we're getting off on a tangent and not really helping the OP.

My suggestion, disconnect the TCCM (located behind the passenger side kick panel directly ahead of the passenger front door. Alternatively you could remove the ATC fuse in the underhood fuse box & the CTSY LP fuse in the IP fuse box. Either event should reset the system and it should shift itself into 2HI when power is restored, I suggest disconnecting the TCCM first as this also allows you to inspect the terminals in the connector at the TCCM as there has been numerous cases of corrosion in these connections.

You can also inspect the 4wd vacuum system for proper operation. There are a number of threads in the Tech Article (DIY) section and throughout the forum with very detailed descriptions of what to look for.

Given that the transfer cases used in these trucks has a 2.72:1 gear ratio for LO range, you should definitely notice the difference. The torque multiplication alone should set you back in the seat much more under acceleration, but you should also notice that the engine speed is 2.72x higher for a given speed than when in HI range; so if you typically drive 60mph with the engine speed of 2000RPM in HI, in LO the engine would be turning 5440RPM just as an example. That should be quite evident.

Let us know what you find and we'll move on from there. Any questions, just ask.

 

I stand corrected... Like I said, shows how often I have to use my 4 wheel drive option...