Transmission shifting weird issue....

I have a 1997 4 door Tahoe with the 5.7L, she has 116,000 on her right now. The problem I am experiencing is mainly at freeway speeds but sometimes at lower speeds.

I am experiencing odd revving when Im at freeway speeds. it goes between 1900 and 2100 rpm and goes back and forth in there... like its searching around.

It all started with my cruise kicking out all on its own, and then cruise just stopped working. I have since pulled the fuse on the cruise but it has not helped.

The problem is sporadic, I notice now that sometimes it stays at the higher rpm now instead of shifting back down.

Could this be my Torque converter lock up.

What I have tried:
new Fuel filter
new MAF(Mass Air Flow) sensor
new airfilter

I have heard that the VSS (Vehicle Speed Sensor) could cause bad shifts.

Anyone have this problem and get it fixed?

Thanks

I'll be interested in this thread because I have had some of the same issues in the past with my Yukon. At highway speeds and hot days, it was like my tranny was shifting in and out of overdrive sporadically. In OD at 70 mph I usually run around 1900 rpms, but my truck would randomly spike up to around 2100 rpms, even though I was on a flat highway.

Funny thing is that it hasn't happened to me since this summer. Seems silly that heat would affect this, but it hasn't been a problem since the outside temperatue has gotten cooler.

I'm anxious to see if it becomes a problem again when the weather starts to heat back up.

If your truck's temp is lower that a certain degree (I don't know what exactly) the computer won't let the tc lock up. If your thermostat is stuck open your truck could be running too cool and that could be the cause for your problem. So watch your coolant temp and see if you need a new thermostat.

If it is knocking out your cruise control as well then then common point between the two is the the brake actuation circuit. Get your self a multimeter and check for proper operation of the combo brake switch it handles lights/TCC/cruise control. It sound like your switch has malfuntioned.

sunlitcomet said:

If it is knocking out your cruise control as well then then common point between the two is the the brake actuation circuit. Get your self a multimeter and check for proper operation of the combo brake switch it handles lights/TCC/cruise control. It sound like your switch has malfuntioned.

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where and how exactly would I do this? Where is the switch and how do I know do I know what it means to be working properly?

Sorry for being so stupid.

Thanks,

Kyle

---------- Post added at 05:31 PM ---------- Previous post was at 05:29 PM ----------

destroyer1362 said:

If your truck's temp is lower that a certain degree (I don't know what exactly) the computer won't let the tc lock up. If your thermostat is stuck open your truck could be running too cool and that could be the cause for your problem. So watch your coolant temp and see if you need a new thermostat.

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What would that temperature be? The heat seems to work fine in the car so I am assuming the car heats up enough?

---------- Post added at 05:51 PM ---------- Previous post was at 05:31 PM ----------

A part number for that part would be nice. The dealer cant seem to find it.

Bowie said:

where and how exactly would I do this? Where is the switch and how do I know do I know what it means to be working properly?

Sorry for being so stupid.

Thanks,

Kyle

---------- Post added at 05:31 PM ---------- Previous post was at 05:29 PM ----------



What would that temperature be? The heat seems to work fine in the car so I am assuming the car heats up enough?

---------- Post added at 05:51 PM ---------- Previous post was at 05:31 PM ----------

A part number for that part would be nice. The dealer cant seem to find it.

Click to expand...

The dealer can't find a thermostat. WOW.

Brake switch is at the top of your brake peddle. At about $9 bucks from the dealer or amazon or part store just replace it. it is an ACDelco D1565E. you will need snap ring pliers and a 11mm (7/16 inch) socket to remove and install it. Should take less then ten minutes to do but I will have you disable the airbag system before hand. Another 10 minutes. You Can Do It. If you just want to replace it instead of getting your hands cramped trying to test it I will post instructions or diagrams. Let me know which way you want to go. Like I said this effects you tcc and cruise. Temperature does not effect cruise control operation.

Hey sunlit, do you think the switch could be the culprit in my situation as well?

Sometimes my cruise control works, sometimes it doesn't. I usually just leave it turned off and don't mess with it. But, if that brake switch affects the operation of the cruise plus the torque converter control, do you think it is possibly malfunctioning or have a short in it?

sunlitcomet said:

The dealer can't find a thermostat. WOW.

Brake switch is at the top of your brake peddle. At about $9 bucks from the dealer or amazon or part store just replace it. it is an ACDelco D1565E. you will need snap ring pliers and a 11mm (7/16 inch) socket to remove and install it. Should take less then ten minutes to do but I will have you disable the airbag system before hand. Another 10 minutes. You Can Do It. If you just want to replace it instead of getting your hands cramped trying to test it I will post instructions or diagrams. Let me know which way you want to go. Like I said this effects you tcc and cruise. Temperature does not effect cruise control operation.

Click to expand...

I would prefer just replace it. Instructions and picts are nice. Anything is appreciated. Thanks for all the help.

sunlitcomet said:

If it is knocking out your cruise control as well then then common point between the two is the the brake actuation circuit. Get your self a multimeter and check for proper operation of the combo brake switch it handles lights/TCC/cruise control. It sound like your switch has malfuntioned.

Click to expand...

We have a winner!! My parents '98 Sub did the same thing, replaced the switch and all was good in the world.

EastTXYukon said:

Hey sunlit, do you think the switch could be the culprit in my situation as well?

Sometimes my cruise control works, sometimes it doesn't. I usually just leave it turned off and don't mess with it. But, if that brake switch affects the operation of the cruise plus the torque converter control, do you think it is possibly malfunctioning or have a short in it?

Click to expand...

Most likely. At any rate if you just started throwing parts at it. it is the most common and least expensive part to start with.