The loss of power may mean it is due for a major tune-up. When was the last time it had new plugs, air filter, distributor cap/rotor and wire set, throttle body and flame trap service?
For the ac problem, check the front of the condenser ( in front of the radiator) and see if it is clean and clear of debris ( bugs, dirt, birds ,slow pedestrians etc). If not, clean off with spray from garden hose. No air flow, no cool. Also check for proper operation of the cooling fan, either viscous coupled or electric. I do not know which one they used in the 91's, but would guess electric. You should also check for correct tension, and the condition, of the ac compressor belt to see if it is slipping.
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Gary Gilliam Sumerduck VA, '94 940 na Regina 160k '86 240 190k