I own a Chevy Venture 1999 V6 3.4 liters with a transmission 4T65E,
When I drive (DRIVE selector) I have a strange behavior with transmission for the 3th gear: it doesn't engage from 2nd gear (2nd skip to 4th/overdrive),
but from 4th it downshift to the 3rd (in the range speed 37 to 43 mph).

basically the issues is resumed in this schema:1 => 2 => 4
4 => 3 => 2 => 1
What could be the cause of this issue?

NB: If I try to drive with selector lever in L3, the transmission remains always in 2nd gear.

How are you determining what gear you are in?

I use my smartphone as virtual dashboard connected to OBD2 with InfoCar app,
I have a detailed situation of Speed/RPM in real time,
and I compared data with this graph to detect at what Speed/RPM correspond the gears:

I'd like to see what the PCM/TCM see when it shifts from 2nd. Does it show it going from 2nd to 4th? Does it shift like that regardless of throttle? Full throttle or light throttle it shifts the same?

I believe the torque converter clutch will play a part in this as well.

I don't know if all 1999 Chevy Ventures had the same final drive ratio. If they did then great. If not then the chart might be off by a bit.

How many miles on this vehicle?

How many miles have you owned this vehicle?

Are there any codes stored in the computer?

Is the Check Engine light on?

My suggestion; print this post then get a helper to read steps then document, then on a straight clear dry road in nice weather with no other traffic around do this:

1. Dead stop in Park
2. Shift to "1"
3. Accelerate gradually until the engine is at 2,500RPM
4. Hold this speed for five seconds
5. Shift to "2"
6. What is the RPM now?
7. Hold this speed for five seconds
8. What is the RPM now?
9. Accelerate gradually until the engine is at 2,500RPM
10. Hold this speed for five seconds
11. Shift to "3"
12. What is the RPM now?
13. Hold this speed for five seconds
14. What is the RPM now?
15. Accelerate gradually until the engine is at 2,500RPM
16. Hold this speed for five seconds
17. Shift to "4"
18. What is the RPM now?
19. Hold this speed for five seconds
20. What is the RPM now?
21. Procedure complete

So after each gear change you are recording the RPM, waiting five seconds, then recording the RPM again. It might be the same every time. Might now. This will help us diagnose.

Report back with the results.

From the InfoCar I can see only Speedometer, RPM, TPS, Coolant Temp. and few other (unuseful) parameters,
I show is going from 2nd to 4th by Speed/RPM comparison.


It shift relative to throttle: At minimum light throttle I can shift around 2800 RPM (42 mph in 2nd), but more I kik the accelerator the shift happens at higher RPM (and speed).


~ 96000 miles


~ 3000 miles


Yes, there is a continuous error code P0171: System too lean, bank 1
The vehicle is equipped with an aftermarket LPG system (because here in EU gas is very expensive,
mostly american car owners use LPG) and probably it needs a re-configuration for properly air/fuel ratio .
I think this error has nothing to do with transmission, right?


Yes, due to error code P0171: I can cancel it (then the yellow Check Engine light disappears)
but after a few Km it (obviously) appears again.


I guess, during the steps, you are meaning shift manually from lower gear to higher during run?
I will try (I never used shift lever manually in that way)

My point with asking about throttle is it NEVER hits 3rd gear, skips it every time?

Yes, that'* what I mean. Slightly reworded:

1. Dead stop in "Park"
2. Manually select "1"
3. Accelerate gradually until the engine is at 2,500RPM
4. Hold this speed for five seconds
5. Manually select "2"
6. What is the RPM now?
7. Hold this speed for five seconds
8. What is the RPM now?
9. Accelerate gradually until the engine is at 2,500RPM
10. Hold this speed for five seconds
11. Manually select "3"
12. What is the RPM now?
13. Hold this speed for five seconds
14. What is the RPM now?
15. Accelerate gradually until the engine is at 2,500RPM
16. Hold this speed for five seconds
17. Manually select "4"
18. What is the RPM now?
19. Hold this speed for five seconds
20. What is the RPM now?
21. Procedure complete

Yes, when accelerating from 2nd gear ever jump to 4th gear,
3th gear is engaged only when I reduce speed from 4th gear.

what if you reduce to 3rd while in 4th gear