1-2 shift valve
The OE 1-2 shift valve in 4T60-E units is prone to wear and side loading because it is made of raw aluminum. The valve tends to stick in place when shifting from 1st to 2nd, and even when the PCM has commanded a 1-2 shift by turning off the A solenoid, the worn OE valve may fail to make the shift because it is stuck in the 1st gear position.
2nd Gear start with light throttle bump back to 1st
OEM valve wears and sticks.
This drop-in replacement valve is hard anodized with annular grooves to reduce sticking and does not require a reamer.
GM General Motors