My '94 Astro Has a Harsh 1-2 Upshift

The wife and daughter complain it jerks their necks- and it is indeed harsh- all othe rshifts feel normal- it has gotten increasingly worse- tranny fluid is good and at proper level- any other hints- would replacing the 1-2 upshift solenoid valve help?- I have a spare from my last tranny that I had to replace shortly before it went out altogether- This tranny has about 150k miles on it. Thanks

There's a bulletin on that, something about the bore expanding after driving 50 or 60 miles and it allows fluid to leak past the valve, (not solenoid) and cause the harsh shift. If it shifts harsh all the time, the bore may be worn, or the valve sticking. Run a google search on harsh 1-2 shift on 4L60 transmission. Wish I could help you more, but that's all I can remember about it.

from an old post in the Blazer forum by ricksza:

4L60-E Automatic Transmission (RPO M30)

Built Prior to January 15, 2000 (Julian Date 0015)

This bulletin is being revised to update VIN Breakpoint Date information and revise the Parts Information table. Please discard Corporate Bulletin Number 01-07-30-023A (Section 07 -- Transmission/Transaxle).

Condition
Some customers may comment on a harsh 1-2 upshift and the Check Engine Light or Service Engine Soon indicator is illuminated.

Diagnosis


Typically, these vehicles will have been driven more than 32,000 km (20,000 mi) before this condition occurs.

The scan tool may show a DTC P1870 set as a history code.

A harsh 1-2 shift or DTC P1870, caused by wear in the control valve body, may be difficult to duplicate when the transmission temperature is below 93°C (200°F).

Cause
The condition may be due to wear in the control valve body. This wear occurs in the bore that contains the TCC isolator and regulator valves, and results in poor, or no, TCC apply.


Important
DTC P1870 is a type B code. The conditions for setting the P1870 DTC must occur on TWO CONSECUTIVE TRIPS (ignition cycles, with a drive cycle) before setting a P1870 history code.
When the conditions for setting DTC P1870 are met (first trip), the PCM commands maximum line pressure and harsh 1-2 shifts are the result.
This may result in a harsh 1-2 shift with no history code if the conditions for setting the DTC required for the second trip are not met, on two consecutive trips (Ignition cycles, with a drive cycle).
When the conditions for setting the DTC are met, on the second consecutive trip, a DTC P1870 is stored as a history code.
When the P1870 code is stored, the PCM will turn on the Service Engine Soon (SES), Check Engine Light (CEL), or Malfunction Indicator Lamp (MIL).

Correction
Install a control valve body with the revised TCC regulator and isolator valves. Refer to the Parts Information table below (two pages of parts depending on year, model, and engine, let me know what you have). These valves are used in all transmissions produced after January 15, 2000 (Julian Date 0015), and all of the service parts currently available through GMSPO contain revised TCC regulator and isolator valves.


Important
If all of the following conditions are true, it is not necessary to rebuild the transmission or to replace additional transmission components beyond the control valve body.

Transmission operation is normal before the transmission reaches operating temperature, or before DTC P1870 is set (no slips, flares, or missing gears).
The torque converter is not blue or overheated.
The transmission fluid is not burned or has no burned odor.
The transmission fluid pan contains no abnormal debris (clutch material, bronze, brass, or metal fragments)

Thanks Eric, that would be the one.