I have been getting really poor gas mileage over the last year or so. It is a 2.4L 20 valve, non-turbo. I used to get 20-22 in the city and upto 29-30 on the hwy. Now it is down to 14-15 city/20 hwy! I put a newer engine in it partly because the original was getting the same results, plus it had other problesm that really needed a better engine at 130K! At the time of engine replacement by a very reliable mechanic it was thoroughly looked over and checked well.
The engine has 66K miles, it is clean, no leaks of any kind at all. Starts and runs very well, a new O2 sensor as of 6 months ago, plugs and wires are only 9 mo. old, oil changes every 2500 miles, front end is aligned.
What am I missing in checking things out? Any other ideas?
Thanks.

I used to commute 30 miles one way, all highway, and was getting 25 mpg on average. Now I am driving 8 miles each way, all city streets, lights, stop-and-go, etc, and only getting 15 mpg. I am not really alarmed by this.
Or should I?

on two engines you get the same results..well unless you have a draggin brake (draging REALLY bad) i say your missing the fact that your driving has changed..

You also might want to consider what parts were carried over from the old engine to the new. Intake manifold, air intake, emitions stuff, accessories.