Power Mode Not Working On A/T

When i push the power mode button,light comes on,but nothing downshifts.I can also floor the gas pedals,no downshifting,but going slowly up a hill,will downshift one gear only.also about this same time,speedometer & cruise control stopped working.
i no nothing of these trucks,so ANY help will be GREATLY appreciated.

what kind of truck what year what engine..

post vital statistics...

it's a 1987 D21 hardbody with SE package-3.0. V6.

read the codes and check to see if it has a kick down cable...