A continuous failure to upshift can point to governor clogging, or valve-body troubles. Intermittent is often electrical (kickdown).

B2 typically causes failure to move forward at all, that is, to shift INTO first gear. Failure to upshift is mostly caused by kickdown system issues: stuck switch (in cabin, under skinny pedal), sticking solenoid (right rear corner at bottom of transmission). You can easily isolate the switch by pulling the relevant fuse ("AT kickdown solenoid). May be 5 or 8? Pulling the fuse does NOT isolate and prove the solenoid itself to be good; it can still act wonky mechanically with no power being supplied. The solenoid can be serviced from under the car, without even removing the pan.

Your flickering brake light (whether it's the e-brake or the "low fluid"/"bad pads" light) is wholly unrelated; there is no CAN bus or other trickery on these cars. Unless the harness has shorted together somewhere. But I don't know if the wires even get physically close anywhere to allow that to happen.

__________________
James Marriott
2003 Buick Regal
1983 300D (228k, frau Auto)
1996 Suburban K2500 (192k, 6.5 turbo diesel/4WD towmaster 10,000)
www.engineeringworks.biz
1987 300SDL junker 170k
1982 300SD junker, 265k