Are you burning it or dripping it? I have an '88 at 245,000 miles that doesn't use a quart between oil changes (5000 mile intervl on synthetic oil), but I replaced the rear main seal around 175,000 or so.
I worked on another '88 for someone last year (actually, I guess it was more like 2 years ago) that was fine around town, but when I set off across the country to deliver it from CT to MT I was blowing about a quart in 600 miles through the rear main seal. Combination of the seal being dried out, and the CCV system being plugged so at highway speed the crankcase was pressurizing and forcing the oil past the old seal.