Transmission Stumbles At Highway Speeds

[burnettw]

Hi and thanks for you help.

 

My stock 96 Yukon SLT 350 with 121K miles runs great around town and below 55mph. Engine is strong, smooth; trans shifts smoothly at all speeds. Within the last 5K miles I have replaced O2's, TPS, Coolant Temp Sens, Cam Pos Sens, distributor, cap, rotor, wires, plugs, fuel filter, air filter, battery. Replaced trans fluid and filter at 60K and 120K miles; minimum sediment; no large particulate matter; no burn odor. Fuel pump pressure tested at 58-60.

 

When traveling in the 55-75 mph range the trans will have a harsh "hiccup" or stumble when in a "no-load," level road condition, or when going over the crest of a hill. Above 75 mph it is less noticeable. Lightly applying the brakes or accelerator, or lifting off the accelerator, will stop it for a few moments. Constantly slowing down or speeding up slightly is the only way to keep going.

 

At 63mph I dropped the trans from Over-Drive to 3rd to test the TC lockup; it turned the hiccup to a slam-bam.

 

All I've noticed is the problem seemed to get significantly worse after I replaced the distributor and CPS.

 

I've never had a check-engine light so have not had a code scan yet.

 

I've considered replacing the trans solenoids dealing with TC lockup.

 

Any and all ideas will be greatly appreciated.

 

Thanks again.

[gmtech4]

no one has responded I think because your complaint is as clear as mud.

 

I would not waste any time here or money on throwing parts at it .

 

get it diag'd by a tranny guy,

 

my 2 cents

[Nytemare]

no one has responded I think because your complaint is as clear as mud.

 

I would not waste any time here or money on throwing parts at it .

 

get it diag'd by a tranny guy,

 

my 2 cents

+1 on Trans shop looking at it

 

But it does sound like TCC solenoid issue.

[rodram]

Hello Bill.... (based on the avatar, we look like twins.....)

 

I agree with these guys, that you should get a transmission diagnosis from someone you can trust....

.. these 4L60E transmissions work great until they wear out .... my 97 crapped out this year at 212,000 km (132,000 miles) and I have been told that I beat the average by a little bit.....

.. I thought it was just solenoids, but after a thorough diagnosis I was assured that I neeeded a total trans and torque converter rebuild.

 

paid the mechanic and it sure works good now.... and with some stronger parts in it