93 Yukon Lugs trying to go from 4th gear lockup to 3rd

[scott2093]

Been meaning to get into an issue I've been having and last night while driving I just happened to have aldl droid running and noticed something.

93 k1500 350 tbi 4l60e....

While I'm in 4th gear lockup, it takes more throttle to get it out of lockup and get going than it should. It'll just lug until I accelerate harder than I should have to. Like I'm trying to make a statement when it finally drops to 3rd. Lockup releases fine if I tap brake.
Driving around in 3rd doesn't seem to have this issue, at least as noticeable but, I think there's a slight hesitation in the same context there too. Will check

Shouldn't it just come out of lockup into 4th or does it have to go to 3rd?

I noticed when this lugging or hesitation happens, the spark advance drops in the single digits and the map readings shoot up.

Now that another member showed me how to record my phone screen data, I plan to make a good recording of data sometime within the next day or so. Attaching a screen shot of the spot when it happens.
Screen space is limited so I wanted to ask what data would be most useful to catch while recording?

I'm thinking it feels like a vacuum leak but idk....

 

[Scooterwrench]

Are you running an aftermarket chip that may be burned for more TPS% and/or MAP to unlock the convertor?

 

[scott2093]

Are you running an aftermarket chip that may be burned for more TPS% and/or MAP to unlock the convertor?

No. Everything is stock apart from cai and tb spacer..hi flow cat...transgo kit..corvette servo..

 

[Scooterwrench]

May want to check those two sensors to see if maybe one is out of spec.

 

[PWC Repair]

Watch TPS voltage as you move the throttle very slowly. Make sure it didn't develop a dead spot.

 

[L31MaxExpress]

Probably just the normal lifeless GM shift patterns. One of the biggest improvements tuning a vehicle is the transmission brhavior.

 

[scott2093]

Probably just the normal lifeless GM shift patterns. One of the biggest improvements tuning a vehicle is the transmission brhavior.

These shifting patterns cause the spark advance and map voltage to act funky? Truck trying to overcome them?

 

[L31MaxExpress]

These shifting patterns cause the spark advance and map voltage to act funky? Truck trying to overcome them?

It is working how GM built it. MAP rises with fairly small throttle increases at low rpm. The factory spark advance is negative at low rpm and high load.

If you were to hook up a vacuum gauge you would find that cruising 60-70 mph in overdrive it does not even take 1/2 throttle to zero out a vacuum gauge.

You can check the TPS output itself to make sure it is right, but GM programmed the TBIs and Vortecs to hold overdrive and lockup to a throttle position that will make the truck a slug compared to throttle input. Not uncommon to see GM hold overdrive and lockup close to 3/4 pedal at normal highway speeds. The 2-1 downshift is the absolute worst on them also. Rolling 10-15 mph it takes near WOT to get back into 1st. The shift pattern and lockup patterns are the absolute worst the way GM built them. The engineers set them to get into overdrive and lockup as quickly as they could, driveability be darned. By comparison the way I set up the shifting makes the truck feel like it has 2x the power in normal driving. The upshifts and downshifts are far more linear and in line with the throttle position, engine rpm, and road speed. Give it 1/2 throttle at 70 mph and it kicks down and actually goes. Give it half throttle from a stop and it runs the tach up to 3,000-3,500 rpm before it grabs another gear.

 

[scott2093]

Makes complete sense and describes my experience ....
It's been like this so long I can't remember if it was ever different like my mind is trying to tell me...
I'll still take a video of some data to see if something else may be happening that's making me think something's off.
Thank you for your breakdown..
and is there a write up on what you did to tune yours?

 

[Scooterwrench]

My old truck is just the opposite,just a little pressure on the go pedal makes the TCC unlock and just a little more pressure causes it to kickdown. I contribute that to a worn out 305 that never had any balls to begin with.