'94 Chevy Camaro only accelerates 40 mph uphill

I have a '94 Camaro. V6. When I take off on a flat road, the car runs fine. But if I take off and immediately start going uphill, pedal to the floor and it only goes 40 til I get to the top. Then it rapidly accelerates up to 50-60. It ran fine on the interstate. It's vibrating more than usual now. We've replaced spark plugs, oil change, cleaned the filter. It has 177k miles on it. Anyone have an idea what's wrong? Thanks in advance.
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Could be a number of things, I might be thinking about fuel filter, coil(s) ,plug wires , usual stuff for a vehicle with age on it