i have an 86 olds cutlass 305 engine misses under load .what could be the cause of this?

Seen this before, not fuel if does not miss going fast. I cured this on x2 GMC vehicles after replacing ignition coils. also if the coil is mounted behind Carburator it may be aching when the load encreases and the coil arcs internally as the voltage needed to develope spark encreases and finds a shorter, easier path encluding the high voltage wires. buy a new coil and wire set and remove wires and install new, one at a time. sgn. Tomtronics..... the Ole Master Chief usn ret