Also don't count these out. From
FATMOE,
Mar 16, 2012
2. 1-2 shift does not happen at WOT until you let off the gas: Best case: try replacing the TPS. Middle case: leak in the 2nd gear apply circuit (servo assembly or 1-2 accumulator). Doublecheck by using the pressure gauge and watch for a big drop when the PCM commands 2nd gear. Worst case: poor line pressure rise (see below).
3. 1-2 Shift shudder at WOT; delayed or abnormal 1-2 shift; There's a problem ONLY on the 1-2 shift: 1-2 accumulator piston cracked or stuck cocked in the bore. Check the yellow spring inside the vacuum housing for breakage. Also, if the accumulator housing walls are scored, the housing must be replaced. Easy fix in the pan.
4. 1-2 shift is delayed and harsh, may not shift into OD: Check TPS for smooth and linear electrical response over the entire range of motion. If not, replace.
5. Trans does not upshift out of first, speedometer reads zero at all times: VSS failure. Easy fix on rear of transmission, but xmember must come out to access VSS.