Acceleration sluggish/pings when hot; FWD model

My car when engine is normal running temp (3:00 on temp guage), accelerates as if I put the cheapest regular unleaded gas in it! I always use name brand 93 octane, but it really struggles when accelerating up steep mountain highway grades. It's just like I had put cheap gas in it. It also does it on flat Florida roads, especially when AC is being used in hot summers, but even when off. Does anybody know a remedy? In mountains, should I downshift to 3rd or 2nd gear? Mine is a front-wheel drive '94 L. Service techs don't know, and I tried 90 octane too, no luck. Been happening for years and worried about mountains now.