Well pal my friend has been in busyness for 12 years and owns 2 Aamco transmission shops in Indianapolis In. I think he knows what he's talking about. Your attitude is the very reason I haven't used this forum in a few years , I see nothing has changed .

 

I don't care how long your "friend" has been in business, nor how many Aamco's he owns; If the trans is not slipping in 4HI, then it is not slipping in 4LO; do you not grasp that concept? As Doc says, the transmission and the transfer case are 2 entirely different components, neither one knows (nor cares) what the other one is doing. That's like saying that if you run out of gas, then your battery must be dead. Huh? This is not attitude, we're simply trying to save you from throwing money away.

Have your friend drive the truck with you in it and show you that it is slipping in both 4HI and 4LO. If he can't, he's lying and there is nothing wrong with the transmission (and he's not your "friend"). The "lunge" that you describe is perfectly normal (and in fact expected) for a 1-2 shift in low range. That shift occurs at only about 3-5mph when you are in 4LO, so the difference is very pronounced.

In fact, try this to prove it to yourself: Put the truck in 4LO, but manually shift the transmission lever into low (1st) and leave it there. Now accelerate as much as you want. The "lunge" will be gone. Why? Because the 1-2 shift will not occur. If the transmission was slipping and then grabbing at higher RPM, as you suggest, then the "lunge" would still be there.