MT/ 4x4 troubleshooting... Help?

Hey guys, I could use some brainstorming. Trying to find the reason behind this weird but not necessarily bad symptom I've noticed with my truck.

First things first. She's an 06 Sport AC, 1GRFE. 251K miles. 3" block lift, 33's. No regear yet.

I've noticed a weird difference between 2WD and 4WD. I've never had any type of problem transitioning between the two. When in 2WD, I feel like there is a bit of a gap or slack somewhere in the drivetrain which makes for a less comfortable transition from acceleration to deceleration, and vice versa. I have little to no play in my driveshaft, U joints were the first thing that came to mind. But, when driving in 4WD, everything feels super tight, like brand new. Transmission practically shifts for me, its that smooth.

What do you think? Where else should I look? Is this just a symptom of her age? Any other info I'm missing?

Thanks in advance guys.
-Steve

 

In my uneducated opinion it sounds like axle wrap which is more pronounced in 2WD as the all the power is going to the rear, where in 4WD it's split. Blocks and craptastic springs contribute to axle wrap. Best fix is a good set of leafs.

 

Hahaha, good to know. A Dakar pack is in my near future, along with coilovers. The block lift was against my better judgement, but necessary at the time with a small budget

 

I agree with this. Most of the problem is probably coming from the block lift. Axle wrap happens, but block lifts are basically levers that make your axles way easier to wrap. I bet if you put a camera below your truck and drove forward/backward/forward/backward you'd see your entire axle swinging front to back like a pendulum.

Block lifts: Just say no!

Edit: Here's a video showing the effect.

https://www.youtube.com/watch?v=hiTRH1N_duo

 

So, to revive this thread in the hopes of helping someone, over time she has gotten steadily worse, even after I put a set of Allpro springs in. I've been able to determine that the issue isn't axle wrap, but my rear diff. Way too much backlash, resulting from worn pinion bearings.