Republic of Texas

Hi guys. Have not posted in a while. I have a 92 truck w/305. 154,500 miles...for about a year it has been clattering under moderate to hard acceleration, on 87 octane gas. I run 91, it does not do it. Now here in Abilene, 91 is the highest we can get. We cannot get 93 octane anymore.Texaco left town, and that went with them. The engine should run fine on 87, but clatters real bad. What can be done to fix this without having to run the high octane? I have also noticed certain brands treat the engine better or worse too. I go thru about 40 gallons a week, and have tried them all, from Fina to Shell, to Citgo....all different characterstics. The best so far is Shell, 89 octane. But its expensive too. I have the factory plug wires still on this truck by the way, if that makes a difference. (old wires...wow)