vibrating when warm

hello gearheads, i own a 1992 S-10 with a 4.3 liter and there is plenty of power when the engine is cold, but when the operating temp. is achieved the engine loses power and there is a noticible vibrating. i am on my way to the ford dealer to get me one of those, please help, could it be the timing? how can i check if the ignition is working properly. i`ve set it at zero with the wire disconected but it wasn`t really of. also, i found that the exhaust is making some pinging noise after i shut the engine down as if it became warmer then normal, fuel went up as well i am at a loss any help is welcome