Here's a question... when my 98 F-150 was new and I'd set the cruise, it would maintain the same speed regardless of the terrain (uphill, downhill etc).

Now, when I set the cruise, it'll lose about 5 miles going uphill before it downshifts and gets back to the speed the cruise was set at.

Any idea what the problem might be???

 

How many mile have you got now? If you've put a lot of miles maybe the truck is just getting tired? Maybe it just needs a good, thourough tune up to bring some life back into it.

 

I doubt it's that. It's only got 55k miles on the motor and the truck runs great. It just lags on hills until it senses that the speed has dropped. I think it's a speed sensor or something else that tells the cruise control how fast the truck is going.

 

Mine did that a while back (before I got the blower). My MAF (mass airflow sensor) was going bad, was sending kooky voltages to the ECU. It would just sorta slowly fall on it's face on long grades. But I never got a code...

You can check your MAF with a simple voltmeter and a shop manual (so you know what voltage it should be sending).

Not sure if this is your problem, but you never know...

If you have an aftermarket air filter with oil on it, the oil can contaminate the wire element within the sensor. In my case, cleaning it didn't help, so I got a re-man MAF at Auto Zone for like $60.