1995 Buick park avenue stuck in 1st... sometimes.

it seems like the tranny clutch pack needs servicing... overhaul time. mine had it around this much miles. vehcile speed sensor (vss) could be intermittent??

Same here but it started at 255680.0 miles. Mine WILL shift when stuck but you have to do this: from a complete stop drive slowly, barely touch the gas/air pedal, and as the traffic behind is going around you, the tranny will shift either at 15mph mark or just after 15mph when you let off the gas at the 15mph mark. IF, you drive slowly up to the 15mph it always shifts, IF you drive faster than this it usually wont shift until you coast to below 15mph. Most of the time you will feel it shift. I've noticed on inclines of even 5%, (and bigger ones too) it has more of a problem shifting. I'll either avoid stops on an incline, (when you even have the choice) drive up the incline and once on level ground turn the car around to make my turn. Both, on level and traveling down hills are fine but the shifting still takes place on the slow takeoffs and at 15mph. Rebuild or replacing the tranny even with a used tranny is what eventually is the fix. Some ppl have said Flushing the transmission a few times 'might' help or extend the rebuild/replacement time. Their 'flushing' was to drain the fluid, refill and drain until you have either used up 1 to 2 gals. of new tranny fluid, replace the tranny filter, and gasket, and refill with new tranny fluid. This is, again, temporary, but extending your rebuild/replacement time might be what you need at the moment.

To eliminate your doubts on the computer replacement part of your question- mine was replaced 4 years ago.