90 LUMINA 3.1 trans. problem

it has more than 150,000 miles and it just wont shift out of first gear i unplug electrical wires from it but still the same, fluid looks and smells ok. Any help or ideas before giving up, thanks guys...

Make sure you have vacuum to the modulator on the trans, 2cnd also scan it and check the tps for proper operation.

Have you tried shifting it manually, putting the shifter in 1, then moving it to 2, etc...? If it shifts manually, then the vacuum modulator is the problem.

Transmission filter would be my first step if it hasn't been changed yet in the last 50K. It should be due anyways if your car has 150K.