Running: on road (undulating) vs on track (flat)

What type of track? Tracks have varying levels of absorbancy. So there's absorption upon footfall and you then have to work harder to push off. There could also be more turns. Run 1 mile straight out and one mile doing 4 or more looped laps. Straight is faster. Hills are definitely harder than flat but there's a certain level of hills that doesn't cause me any significant change and downhills recover you and speed you up. I do know when I'm reaching elevation rises beyond my happy place though.
And it could all just be coincidence too. Some days I can run 6 miles at a 30 second faster or slower pace than another day at the same heart rate.

Track should be faster. it was designed for running.

Running in a circle is a mind game. Keep at it and you'll get faster.

The fastest road mile I've run in the last year was a 5:49...on a track I ran a 5:28 1600m (30ft short of a mile.)

I would think running on a track would be faster. For me, though, track running would be slower due to the demoralizing forces of boredom. Just sucks the energy and drive right out of me. I prefer trails.

I'd agree an outdoor 400 track should be fast. I do my speed work on outdoor highschool tracks and love it, well aside from the whole hamster on a wheel aspect when your not running fast enough to forget about it. Indoor gym tracks I have found to be slower. Lots of tight curves with a shorter lap and I do not like the absorption at our local indoor... I really would consider coincidence. I wouldnt think the mind play of doing laps should affect your heart rate, as you said you were working just as hard on the track for a slower pace.

I use runtastic on my phone with GPS and with a heart rate monitor strap.

I just checked the GPS map I ran today and notice that the route sometimes did not follow the turns closely. instead of route being oval like the track, sometimes it's more like a rectangle (if you know what i mean). Does that mean I may have run more than the GPS told me? (I ran 24 laps on lane 5 [lane 1 being innermost])

Yeah, Likely by a fair bit. GPS's can't handle small circles.
Also, running in the outerlane will add about 10m to each lap, so you actually finished at 10K around 1/3 of the way around lap 23.

thanks all. Is there a good device to measure pace & distance for running on track?

The track is already measured. All you need is a stop watch.

Use Google Earth or similar satellite map program to carefully plot the points around and make one lap. It may not come out to an exact round number, (e.g. 402m) but you can clearly tell that this would be a 400m track.
Your track is almost certainly 400m around. 4 laps makes 1600m (essentially a mile)

use a digital wrist watch to measure the time taken for each 'split'.....be it one lap or 4 (one mile). that's your pace.

This has been the standard since the late 1940's when stopwatches were invented and it isn't likely to change.