I have a 94 Pontiac Firebird with a 4L60E automatic transmission. I bought a transmission rebuild kit and installed everything right, but it's not shifting into second the way it should. Everything in the kit was installed. All the gears new, oil new, filter, but the stator seal I had to replace. I don't know what it can be.
It sounds like the 1-2 and 2-3 (A/B) shift solenoids are continuing to be energized or are stuck in the on position. According to the 1994 Camaro/Firebird Service Manual (pg 7A-14A-6):
The PCM energizes each solenoid by grounding it through an internal quad driver. This sends current through the coil winding in the solenoid and moves the interal plunger out of the exhaust position. When 'ON', the solenoid redirects fluid to move a shift valve.
In order for the transmission to be in first gear only, both of these need to be energized, which makes me wonder: are you sure it's in first gear and not third gear? This could also be the case, mainly because 3rd gear happens when both solenoids are off. The general layout for the shift to solenoid operation looks thus:
Gear | Shift Solenoid | 2-4 BAND | FW Sprag
| 1-2 | 2-3 | |
1st | ON | ON | | HOLDING
2nd | OFF | ON | APPLIED | HOLDING
3rd | OFF | OFF | | HOLDING
4th | ON | OFF | APPLIED |
Also, is there a check engine light which might be on? If so, get this read, as it will tell you if one of the solenoids is not operating correctly.
Did you get the electrical connector reseated properly? There are a dozen or so pins in the connector, one of which may have become bent when reinstalled. Pull the connector and ensure there aren't any major issues with dirt, crap, or bent pins (if for not other reason than to eliminate this as an issue).
Beyond that, without more information, I'd be at a loss.