Odd clutch behavior - 2nd Gen - slipping only in 4th?

I was convined that I had one of those known 2nd Gen clutch problems, but the behavior is puzzling me.

Details:
2010 Access cab, 2.7L, 5 speed, 130,000 miles. I have 32” tires and never regeared. The gear ratio is a little high and does abuse the clutch when taking off uphill or in deep snow.

My clutch is fine, except for 2 years ago I noticed some slippage on the tach... Only in freezing temps and only at high speed on the highway. Basically, the only time it happens is when I'm in 4th, and press the gas hard before upshifting. The tach jumps 500rpms then the speedo slowly catches up.

The part that puzzles me is that I have no problems when abusing the clutch in the lower gears, when it SHOULD slip.

For example, the same day I saw slippage on the interstate, I was able to pull a full sized truck out of a snowbank while in 4-Low. He was stuck hard and I was spinning/wheel-hopping for a minute or so before he budged. If bad, the clutch should have slipped some then, I would think.

One possible variable: could the cold air at high speeds be cooling the clutch and flywheel off... Causing the issue only at those speeds?

I don't know and am looking for input before I put a new flywheel and clutch in. I hope I'm missing something simple.

 

The easiest way to tell if a clutch is slipping is to run 2nd or 3rd gear to near redline and then aggressively shift to 5th.
The gear ratios in the lower gears (incl low range) multiplies the torque to the wheels so there's not as much load on the clutch.
4th gear is usually 1:1 so more engine torque is req'd for the load and since that power goes through the clutch you get slipping.

 

Clutch friction discs need replacing. The pressure finger diaphragm may need replacing too.

 

Clutches will begin slipping first in high gears when they start to wear out and not low gears. You've got it backwards. Your clutch is on the way out.

 

This! A lot more counter torque applied to the clutch disc in higher gears, so when you romp on the throttle in a higher gear that's where you'll notice the slip first. In a lower gear, the counter torque applied to the clutch disc is low because the lower gear ratios of the trans/transfer case is helping you out.

 

Purely on math, all of your answers make sense, despite "feeling" backwards to me. And I appreciate it. I was just in denial that it was a tach/sensor issue because I do not want to drop the transmission/transfer case this winter.

It is still hard to believe (from perception only) that the 2.7L put more force on the clutch (just by acceleration & while in motion) than grabbing/jumping hard while pulling on the static weight of the stuck truck.

Looks like I will be shopping for parts!