99 Silverado transmission slipping???

[jeverett]

I've got a 99 Z71 5.3L with about 87K on it now. Within the last few months, I've noticed when I'm just driving normally, not giving it hell or anything, the truck shifts fine from 1-2, 2-3, but then when it gets to the 3-4 shift, it seems like it shifts, goes back into 3rd, then shifts again back into 4th. I've thought about changing the filter and fluid, but not sure if it would help. I un-installed the Hypertech and tried it, and it still does the same thing. Other than this, it seems to shift fine. It went from doing this ocassionally, to doing it nearly every shift fron 3-4.
What could be causing it to do this?

Oh yeah, I've checked the fluid and its dead on the correct level, and looks and smells as if it was new.

[Jimmiz71]

Jayson right now I'm in need of replacing my shift selonoids, I'm just waiting for them to arrive from GM, anyways I posted a thread on monday cause i got a light and when i used my scan tool it came up as shift selonoid, I didnt think my truck was shifting diferently till I got on the highway and my truck was shifting in and out of 4th gear and I got off the next exit and took back roads Im convinced its my 3-4 selonoid thats not working right.. Hopefully chevy will have them for me so I can change them this weekend,
Just an idea.. -Jimmy

[Gooseneck]

Are you sure it's down shifting to 3rd or is it the torque convertor going in and out of lock-up. Inspect your trans fluid and make sure that engine coolant is not mixing from a faulty cooler.

[sully16]

I also have a similar problem with the 3-4 shift however my is a little different. I have a 99 Z71 ext cab, once the truck is warmed up and I am on the highway it seems to shift into 4th too quickly (at about 35-40 mph) and then the opposite when I am slowing down it takes too long to go down into 3rd. What happens quite often is as I am driving along if I need to slow down coming into a corner to about 35mph the truck stays in 4th, the rpm's drop to 900-1000, then I come out of the corner and put the throttle down maybe 20-30% and the truck stays in 4th, the rpm's stay way too low at 900-1000 and the truck starts to shudder quite a bit because the rpm's are too low. What I do then is hit the throttle down hard 70-90% and this kicks the tranny down to 2nd, the rpm's shoot up to about 2500. Does anyone think that this is also the 3-4 solenoid? I have done the obvious and checked the fluid, I changed the fluid and filter last summer, I checked and have no codes stored. Like I said this only happens once the truck is warmed up, when cold the tranny shifts just fine. It also shifts normal when in tow/haul mode. Any help would be greatly appreciated.

[jeverett]

Originally Posted by Gooseneck

Are you sure it's down shifting to 3rd or is it the torque convertor going in and out of lock-up. Inspect your trans fluid and make sure that engine coolant is not mixing from a faulty cooler.

I'm pretty sure its not the torque converter, it does all of this before the converter locks in.

It almost seems as if when going to 4th, for some reason it thinks it needs to downshift back to 3rd, then immediately back to 4th... then a bit later the torque converter locks..well after its in 4th gear.

[auto5023]

Originally Posted by jeverett

I'm pretty sure its not the torque converter, it does all of this before the converter locks in.

It almost seems as if when going to 4th, for some reason it thinks it needs to downshift back to 3rd, then immediately back to 4th... then a bit later the torque converter locks..well after its in 4th gear.

I have a 2000 Z71 doing the same thing. Let us know if you find the problem.