stuttering between 35-50mph 2.8L

I have an 88' olds cutlass supreme with the 2.8L in it. it strarts fine idles ok, but at 35-50 mph it wants to fall on its face. now let me clarify that it does it while trying to maintain a speed between 35-50mph not while accelerating through it. at highway speeds it ok. i have replaced the plugs,wires,fuel filter. anyone have any ideas? i just bought injectors but i want some opinions before i put them in. oh and i took it to the tranny shop and its not the tcc sensor or lock-up problem. any info would be greatly appreciated
thanks

hi there

You might want to check your plug wires and make sure they have good separation from the engine block and each other. It is also possible that you have a coil pack going bad.