Verified answer

1985 was a terrible year for vacuum hoses, and solenoids everywhere.

It could be an EGR problem, or plugged fuel filter.

Or any number of problems.

Weak cylinder? doubt it.

Other reasons include a bad catalytic converter, ignition misfire and resulting knock sensor activation which retards the timing and causes a loss of power. Try driving it in "drive" only without overdrive engaged to keep the engine RPMs higher. That should increase your power for now. Of course you've changed all the basic maintenance items like the air filter, fuel filter, PCV valve etc. When you change the plugs, use original equipment AC Delco, and before you install any new plugs, do a compression check on each cylinder. Also check the distributor spark advance operation. One tip off to the diagnosis is how often the engine oil was changed by prior owners. If you remove one of the valve covers, you can start to get an idea of how well the engine was maintained. If you see a lot of black oil sludge deposits under the valve cover, you'll know your in for the kind of repairs mentioned above.

Start with a basic tune up. Check all vacuum lines, change fuel filter/ air filter. While you have the plugs out compare them, you want them to be tan. White plugs mean your running lean (to much air, it's bad). Black powder looking plugs mean to much fuel, and wet black plugs means your burning oil. The plugs should look the same, one cylinder that looks different means their is a problem there. Good luck.

i own a repair shop,and those were good for wearing timing chains and gears out in them,and also cam shafts too,all of this was made of a soft metal and they wear out in about 100 thousand miles or less,the after market ones that you buy will be real good there made of a better metal and they last really good,but that would be the first two major things that i would check out on it,it will help you start narrowing a lot of it down good luck hope this helps.