95 Mercury Villager Check Engine Light

Last two weeks, my 95 Mercury Villager (79,000 miles) is displaying
Check Engine
Light on. This typically happens when I am driving up a mild uphill slope at highway speed (above 55 mph). Mostly the light disappears at the end of the slope, or if I slow down. The check engine light never shows up in city driving, or on level highways. I got a mechanic look under the hood. The EGR/BPT hose is fine. Fuel pressure pump, gas cap, crankshaft, timing belts are okay (these are the usual suspects).
Before heading to the dealer, is there anything else that I could look into ? Does the fact that this light shows up only on uphill at highway speed give any clues ?

First of all, you did NOT go to a mechanic. If you had, he would've discovered an error code stored in the vehicle's computer, and that would at least be a clue. You need to see a real mechanic, and it doesn't necessary have to be the dealer.

Now, for a guess: If the code shows a problem with the throttle position sensor, and there are no other symptoms, you can ignore it for the time being. I had this problem with my 92 Taurus, and a friend had the same problem with his 99 F-150 pickup. In my case, it lasted 6 years. Finally, I noticed that in slow traffic, I was having difficulty maintaining very slow speeds. In other words, if I wanted to accelerate from 10mph to 15mph, the car wanted to go directly to 25mph. It was like trying to control the volume on a radio with a dirty volume control. My mechanic and dealer both said the tps had nothing to do with this issue, but neither could point to any other reason, so I had the tps replaced. It solved the problem.

So, get an error code reading after the next time the check engine light comes on, and keep notes on the codes. Come back here and report the code, too.

I'm not a mechanic, by the way, just a guy who owned a Ford for 10 years.